Update coding style after pycodestyle 2.1.0

In pycodestyle 2.1.0, E305 was introduced, which requires two blank
lines after top level declarations, too.

See https://github.com/PyCQA/pycodestyle/issues/400

See also #10689; thanks @stepshal for first mentioning this issue and
initial patches

test/test_youtube_lists.py

@@ -66,5 +66,6 @@ class TestYoutubeLists(unittest.TestCase):
         for entry in result['entries']:
             self.assertTrue(entry.get('title'))
 
+
 if __name__ == '__main__':
     unittest.main()