Fix incorrect reference link in collections module

Fix incorrect reference link in Lib/collections/__init__.py

The reference link to the multiset tutorial was incorrect in Lib/collections/__init__.py.  
Updated it to match the correct link already used in Doc/library/collections.rst.

Author: reddevilmidzy

Lib/collections/__init__.py

@@ -595,7 +595,7 @@ class Counter(dict):
     # References:
     #   http://en.wikipedia.org/wiki/Multiset
     #   http://www.gnu.org/software/smalltalk/manual-base/html_node/Bag.html
-    #   http://www.demo2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm
+    #   http://www.java2s.com/Tutorial/Cpp/0380__set-multiset/Catalog0380__set-multiset.htm
     #   http://code.activestate.com/recipes/259174/
     #   Knuth, TAOCP Vol. II section 4.6.3