first plot item can be Symbol (no quote)

masa16 · masa16 · commit c994f76244e5 · 2017-08-01T14:32:00.000+09:00
diff --git a/lib/numo/gnuplot.rb b/lib/numo/gnuplot.rb
@@ -726,7 +726,7 @@ def parse_items
       if !@options
         if @items.empty?
           return
-        elsif @items.first.kind_of? String
+        elsif @items.first.kind_of?(String) || @items.first.kind_of?(Symbol)
           @function = @items.first
           @options = @items[1..-1]
           if (o=@items.last).kind_of? Hash
