(overview) Improve one statement, add 's for user perspective.

Author: dongxuwang

_overviews/collections-2.13/introduction.md

@@ -91,5 +91,5 @@ Furthermore, the `partition` operation is quite fast, and can
 be even faster on parallel collections on multiple cores.
 
 This document provides an in depth discussion of the APIs of the
-Scala collections classes from a user perspective.  It takes you on
+Scala collections classes from a user's perspective.  It takes you on
 a tour of all the fundamental classes and the methods they define.