Update gunicorn to 19.9.0
Created by: pyup-bot
This PR updates gunicorn from 19.7.1 to 19.9.0.
The bot wasn't able to find a changelog for this release. Got an idea?
Links
- PyPI: https://pypi.org/project/gunicorn
- Changelog: https://pyup.io/changelogs/gunicorn/
- Homepage: http://gunicorn.org