Forced to use the gunicorn version on Github.

Reason: gunicorn maintainers no longer give a fuck about their project
and they aren't letting anybody take over either - see
https://github.com/benoitc/gunicorn/pull/2581

This is not how a FOSS project should be run. A project with 9k stars
and countless usages shouldn't end up in a situation where users beg for
two years for a new release that fixes a bad regression and a bad
security vulnerability. The way gunicorn is maintained and run is an
insult to the whole FOSS community.

setup.py

@@ -66,7 +66,7 @@ setup(
         'eventlet',
         'flask',
         'frozendict',
-        'gunicorn',
+        'gunicorn @ https://github.com/benoitc/gunicorn/tarball/master',
         'marshmallow',
         'marshmallow_dataclass',
         'python-dateutil',