Updated the gunicorn worker to work with gunicorn 19.1

The gunicorn commit https://github.com/benoitc/gunicorn/commit/2b2725dddb6e54c3328524e4efa52b544fd77841 changed the signature of the factory method for the gaiohhtp worker to take one parameter `addr` instead of the `host, port` parameters used before. 
This commit updates the aiopyramid code to match that change.