fix imports

synapse/visibility.py

@@ -17,6 +17,7 @@ import logging
 import operator
 
 import six
+
 from twisted.internet import defer
 
 from synapse.api.constants import EventTypes, Membership

tests/test_visibility.py

@@ -19,6 +19,7 @@ from twisted.internet.defer import succeed
 
 from synapse.events import FrozenEvent
 from synapse.visibility import filter_events_for_server
+
 import tests.unittest
 from tests.utils import setup_test_homeserver