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_http.py

@@ -169,5 +169,6 @@ class TestProxy(unittest.TestCase):
         # b'xn--fiq228c' is '中文'.encode('idna')
         self.assertEqual(response, 'normal: http://xn--fiq228c.tw/')
 
+
 if __name__ == '__main__':
     unittest.main()