Update gunicorn to 19.7.1

[pyup-bot]

There's a new version of gunicorn available.
You are currently using 19.7.0. I have updated it to 19.7.1

These links might come in handy: PyPI | Changelog | Homepage

Changelog

19.7.1

===================

• fix: continue if SO_REUSEPORT seems to be available but fails (:issue:1480)
• fix: support non-decimal values for the umask command line option (:issue:1325)

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖

[coveralls]

Coverage remained the same at 81.553% when pulling 088d5c0 on pyup-update-gunicorn-19.7.0-to-19.7.1 into a334864 on master.