Use keys iterator

Signed-off-by: Michal Čihař <michal@cihar.com>

weblate/trans/views/edit.py

@@ -73,7 +73,7 @@ def cleanup_session(session):
     Deletes old search results from session storage.
     '''
     now = int(time.time())
-    for key in session:
+    for key in session.keys():
         value = session[key]
         if (key.startswith('search_')
                 and (not isinstance(value, dict) or value['ttl'] < now)):