Modified CollectionAssociation to refer to the new class name.

activerecord/lib/active_record/associations/collection_association.rb

@@ -4,7 +4,7 @@ module ActiveRecord
   module Associations
     # = Active Record Association Collection
     #
-    # AssociationCollection is an abstract class that provides common stuff to
+    # CollectionAssociation is an abstract class that provides common stuff to
     # ease the implementation of association proxies that represent
     # collections. See the class hierarchy in AssociationProxy.
     #