fix grammar in collections tour intro

SethTisue · SethTisue · commit 82d01043bb03 · 2015-08-19T17:04:12.000-04:00
thanks Pedro Furlanetto for spotting it
diff --git a/overviews/collections/introduction.md b/overviews/collections/introduction.md
@@ -92,5 +92,5 @@ collections have been released
 as part of Scala 2.9.)
 
 This document provides an in depth discussion of the APIs of the
-Scala collections classes from a user perspective.  They take you on
-a tour of all the fundamental classes and the methods they define.
+Scala collections classes from a user perspective.  It takes you on
+a tour of all the fundamental classes and the methods they define.
