Merge pull request #446 from SethTisue/little-grammar-fix

fix grammar in collections tour intro

Author: SethTisue

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.