fix formatting

Author: Michał Szymański

test/test_closed_streams.py

@@ -186,6 +186,7 @@ def test_receive_window_update_on_closed_stream(self, frame_factory):
         events = c.receive_data(window_update_frame.serialize())
         assert not events
 
+
 class TestStreamsClosedByEndStream(object):
     example_request_headers = [
         (':authority', 'example.com'),