Update DummyHTTPClient.get_context_factory() for Twisted 15.0.0.
Update DummyHTTPClient.get_context_factory() for Twisted 15.0.0.

vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,TouK/vumi,harrissoerja/vumi,vishwaprakashmishra/xmatrix,harrissoerja/vumi,TouK/vumi