Fix 'USER started following USER' activity

It was saying the follower's name twice instead of the follower's name
and then the followee's name, e.g.
Sean Hammond started following Sean Hammond,
fix to Sean Hammond started following Joe Admin.

ckan/lib/activity_streams.py

@@ -18,7 +18,7 @@ def get_snippet_actor(activity, detail):
 
 def get_snippet_user(activity, detail):
     return literal('''<span data-module="user-context" data-module-id="%s">%s</span>'''
-        % (activity['user_id'], h.linked_user(activity['user_id'], 0, 20))
+        % (activity['object_id'], h.linked_user(activity['object_id'], 0, 20))
         )
 
 def get_snippet_dataset(activity, detail):