Use zope.interface decorator

This not only makes code more pleasent to read,
but also makes the code python 3 compatible
(while maintaining python 2 compatibility).

CHANGES.rst

@@ -10,7 +10,8 @@ New:
 
 Fixes:
 
-- *add item here*
+- Use zope.interface decorator.
+  [gforcada]
 
 
 3.0.6 (2016-01-08)

plone/portlet/collection/collection.py

@@ -12,7 +12,7 @@
 from zExceptions import NotFound
 from zope import schema
 from zope.component import getUtility
-from zope.interface import implements
+from zope.interface import implementer
 import random
 
 COLLECTIONS = []
@@ -83,15 +83,14 @@ class ICollectionPortlet(IPortletDataProvider):
         default=True)
 
 
+@implementer(ICollectionPortlet)
 class Assignment(base.Assignment):
     """
     Portlet assignment.
     This is what is actually managed through the portlets UI and associated
     with columns.
     """
 
-    implements(ICollectionPortlet)
-
     header = u""
     limit = None
     random = False