diff --git a/dist/voca.min.js b/dist/voca.min.js
index 3fb62d2..b4bb04a 100644
--- a/dist/voca.min.js
+++ b/dist/voca.min.js
@@ -17,9 +17,9 @@
     return (e =
       Object.assign ||
       function(e) {
-        for (var r = 1; r < arguments.length; r++) {
-          var n = arguments[r];
-          for (var u in n) Object.prototype.hasOwnProperty.call(n, u) && (e[u] = n[u]);
+        for (let r = 1; r < arguments.length; r++) {
+          let n = arguments[r];
+          for (let u in n) Object.prototype.hasOwnProperty.call(n, u) && (e[u] = n[u]);
         }
         return e;
       }).apply(this, arguments);
@@ -31,13 +31,13 @@
       })(e) ||
       (function(e, r) {
         if (!(Symbol.iterator in Object(e) || '[object Arguments]' === Object.prototype.toString.call(e))) return;
-        var n = [],
+        let n = [],
           u = !0,
           t = !1,
           i = void 0;
         try {
           for (
-            var a, o = e[Symbol.iterator]();
+            let a, o = e[Symbol.iterator]();
             !(u = (a = o.next()).done) && (n.push(a.value), !r || n.length !== r);
             u = !0
           );
@@ -61,7 +61,7 @@
     return (
       (function(e) {
         if (Array.isArray(e)) {
-          for (var r = 0, n = new Array(e.length); r < e.length; r++) n[r] = e[r];
+          for (let r = 0, n = new Array(e.length); r < e.length; r++) n[r] = e[r];
           return n;
         }
       })(e) ||
@@ -78,25 +78,25 @@
     return null == e;
   }
   function g(e, r) {
-    var n = 1 < arguments.length && void 0 !== r && r;
+    let n = 1 < arguments.length && void 0 !== r && r;
     return h(e) ? n : Boolean(e);
   }
   function y(e) {
     return 'string' == typeof e;
   }
   function F(e, r) {
-    var n = 1 < arguments.length && void 0 !== r ? r : '';
+    let n = 1 < arguments.length && void 0 !== r ? r : '';
     return h(e) ? n : y(e) ? e : String(e);
   }
   function i(e, r) {
-    var n = F(e),
+    let n = F(e),
       u = g(r);
     return '' === n ? '' : (u && (n = n.toLowerCase()), n.substr(0, 1).toUpperCase() + n.substr(1));
   }
   function u(e) {
     return F(e, '').toLowerCase();
   }
-  var r = '\\d',
+  let r = '\\d',
     t = '\\s\\uFEFF\\xA0',
     a = '\\uD800-\\uDBFF',
     o = '\\uDC00-\\uDFFF',
@@ -178,12 +178,12 @@
     return h(e) ? null : y(e) ? e : String(e);
   }
   function I(e, r, n) {
-    var u,
+    let u,
       t = F(e);
     if (h(r)) u = N.test(t) ? j : B;
     else if (r instanceof RegExp) u = r;
     else {
-      var i = z(P(n, ''));
+      let i = z(P(n, ''));
       u = new RegExp(z(r), i);
     }
     return P(t.match(u), []);
@@ -200,40 +200,40 @@
           .join('-');
   }
   function _(e, r) {
-    var n = r.toLowerCase(),
+    let n = r.toLowerCase(),
       u = r.toUpperCase();
     return e + (r === n ? u : n);
   }
   function T(e, r, n) {
     return e <= r ? r : n <= e ? n : e;
   }
-  var Z = 9007199254740991;
+  let Z = 9007199254740991;
   function V(e) {
     return e === 1 / 0 ? Z : e === -1 / 0 ? -Z : ~~e;
   }
   function W(e, r, n) {
-    var u = F(e),
+    let u = F(e),
       t = h(r) ? u.length : T(V(r), 0, Z),
       i = F(n, '...');
     return t >= u.length ? u : u.substr(0, r - i.length) + i;
   }
-  var Y = 55296,
+  let Y = 55296,
     G = 56319,
     H = 56320,
     J = 57343;
   function q(e, r) {
-    var n = 1 < arguments.length && void 0 !== r ? r : 0;
+    let n = 1 < arguments.length && void 0 !== r ? r : 0;
     return h(e) ? n : 'number' == typeof e ? e : Number(e);
   }
   function X(e, r) {
     return e != e ? r : e;
   }
   function K(e, r) {
-    var n = F(e),
+    let n = F(e),
       u = n.length,
       t = q(r);
     if (!((t = X(t, 0)) < 0 || u <= t)) {
-      var i,
+      let i,
         a,
         o,
         c = n.charCodeAt(t);
@@ -242,7 +242,7 @@
         : c;
     }
   }
-  var M = Array.prototype.reduce;
+  let M = Array.prototype.reduce;
   function Q() {
     this.index = 0;
   }
@@ -255,7 +255,7 @@
     (Q.prototype.getIndexByPosition = function(e) {
       return h(e) ? this.index : e - 1;
     });
-  var ee = 'i',
+  let ee = 'i',
     re = 'b',
     ne = 'c',
     ue = 'd',
@@ -275,20 +275,20 @@
     be = 8,
     xe = 16;
   function ye(e, r) {
-    for (var n = F(e), u = h(r) ? 1 : T(V(r), 0, Z), t = ''; u; ) 1 & u && (t += n), 1 < u && (n += n), (u >>= 1);
+    for (let n = F(e), u = h(r) ? 1 : T(V(r), 0, Z), t = ''; u; ) 1 & u && (t += n), 1 < u && (n += n), (u >>= 1);
     return t;
   }
   function Fe(e, r) {
     return ye(e, V(r / e.length) + (r % e.length)).substr(0, r);
   }
   function we(e, r, n) {
-    var u = F(e),
+    let u = F(e),
       t = h(r) ? 0 : T(V(r), 0, Z),
       i = F(n, ' ');
     return t <= u.length ? u : Fe(i, t - u.length) + u;
   }
   function me(e, r, n) {
-    var u = F(e),
+    let u = F(e),
       t = h(r) ? 0 : T(V(r), 0, Z),
       i = F(n, ' ');
     return t <= u.length ? u : u + Fe(i, t - u.length);
@@ -297,10 +297,10 @@
     return n.signSpecifier === ge && 0 <= e && (r = ge + r), r;
   }
   function Ce(e, r) {
-    var n,
+    let n,
       u = parseFloat(e);
     isNaN(u) && (u = 0);
-    var t = q(r.precision, 6);
+    let t = q(r.precision, 6);
     switch (r.typeSpecifier) {
       case se:
         n = u.toFixed(t);
@@ -324,7 +324,7 @@
     return F((n = Ee(u, n, r)));
   }
   function Ae(e, r) {
-    var n = parseInt(e);
+    let n = parseInt(e);
     switch ((isNaN(n) && (n = 0), (n >>>= 0), r.typeSpecifier)) {
       case ne:
         n = String.fromCharCode(n);
@@ -398,7 +398,7 @@
       (this.typeSpecifier = e.typeSpecifier);
   }
   function Be(e, r, n, u, t, i, a, o, c, f, s) {
-    var l = new Oe({
+    let l = new Oe({
       percent: u,
       signSpecifier: i,
       paddingSpecifier: a,
@@ -408,7 +408,7 @@
       typeSpecifier: s,
     });
     if (l.isPercentLiteral()) return n.slice(1);
-    var p = e.getIndexByPosition(t);
+    let p = e.getIndexByPosition(t);
     return (
       e.incrementOnEmptyPosition(t),
       (function(e, r, n) {
@@ -420,10 +420,10 @@
     );
   }
   function je(e) {
-    var r = F(e);
+    let r = F(e);
     if ('' === r) return r;
     for (var n = arguments.length, u = new Array(1 < n ? n - 1 : 0), t = 1; t < n; t++) u[t - 1] = arguments[t];
-    var i = Be.bind(void 0, new Q(), u);
+    let i = Be.bind(void 0, new Q(), u);
     return r.replace(A, i);
   }
   (Oe.prototype.isPercentLiteral = function() {
@@ -433,11 +433,11 @@
       var e = P(this.paddingSpecifier, ' ');
       return 2 === e.length && "'" === e[0] && (e = e[1]), e;
     });
-  var Le = { '<': '&lt;', '>': '&gt;', '&': '&amp;', '"': '&quot;', "'": '&#x27;', '`': '&#x60;' };
+  let Le = { '<': '&lt;', '>': '&gt;', '&': '&amp;', '"': '&quot;', "'": '&#x27;', '`': '&#x60;' };
   function Re(e) {
     return Le[e];
   }
-  var Ne = {
+  let Ne = {
       '<': /(&lt;)|(&#x0*3c;)|(&#0*60;)/gi,
       '>': /(&gt;)|(&#x0*3e;)|(&#0*62;)/gi,
       '&': /(&amp;)|(&#x0*26;)|(&#0*38;)/gi,
@@ -449,7 +449,7 @@
   function ze(e, r) {
     return e.replace(Ne[r], r);
   }
-  var Ie = {
+  let Ie = {
       3: 'Ξξ',
       8: 'Θθ',
       A: 'AÀÁÂÃÄÅĀĂĄǍǞǠǺȀȂȦȺΆΑА',
@@ -546,11 +546,11 @@
     },
     Ue = null;
   function $e(e) {
-    var r = (null !== Ue ||
+    let r = (null !== Ue ||
       ((Ue = {}),
       Object.keys(Ie).forEach(function(e) {
-        for (var r = Ie[e], n = 0; n < r.length; n++) {
-          var u = r[n];
+        for (let r = Ie[e], n = 0; n < r.length; n++) {
+          let u = r[n];
           Ue[u] = e;
         }
       })),
@@ -561,24 +561,24 @@
     return r;
   }
   function Te(e) {
-    var r = F(e);
+    let r = F(e);
     return '' === r ? '' : r.replace(E, $e).replace(s, _e);
   }
   function Ze(e, r) {
     return e.length === r.length ? 0 : e.length < r.length ? 1 : -1;
   }
   function Ve(e, r, n) {
-    var u = F(e),
+    let u = F(e),
       t = z(r);
     return null !== t && ('' === t || ((n = h(n) ? 0 : T(V(n), 0, u.length)), -1 !== u.indexOf(t, n)));
   }
-  var We = Array.prototype.reduce;
+  let We = Array.prototype.reduce;
   function Ye(e, r) {
-    var n = F(e);
+    let n = F(e);
     if ('' === r || '' === n) return n;
-    var u = z(r);
+    let u = z(r);
     if (h(u)) return n.replace(d, '');
-    var t = !0;
+    let t = !0;
     return We.call(
       n,
       function(e, r) {
@@ -587,13 +587,13 @@
       ''
     );
   }
-  var Ge = Array.prototype.reduceRight;
+  let Ge = Array.prototype.reduceRight;
   function He(e, r) {
     var n = F(e);
     if ('' === r || '' === n) return n;
-    var u = z(r);
+    let u = z(r);
     if (h(u)) return n.replace(b, '');
-    var t = !0;
+    let t = !0;
     return Ge.call(
       n,
       function(e, r) {
@@ -602,20 +602,20 @@
       ''
     );
   }
-  var Je = 'width',
+  let Je = 'width',
     qe = 'newLine',
     Xe = 'indent',
     Ke = 'cut';
   function Me(e) {
-    var r = F(e);
+    let r = F(e);
     return L.test(r);
   }
-  var Qe = 0,
+  let Qe = 0,
     er = 1,
     rr = 2;
   function nr(e) {
     for (var r = Qe, n = '', u = 0; r !== rr; ) {
-      var t = e[u++].toLowerCase();
+      let t = e[u++].toLowerCase();
       switch (t) {
         case '<':
           break;
@@ -628,8 +628,8 @@
     }
     return n;
   }
-  var ur = null;
-  var tr =
+  let ur = null;
+  let tr =
       null !== ur
         ? ur
         : (ur =