Bump gunicorn from 18.0 to 19.5.0

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 18.0 to 19.5.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@18.0...19.5.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -3,6 +3,6 @@ python-twitter==0.8.2
 markdown==2.0.3
 git+git://github.com/dominno/django-moderation.git
 django-recaptcha-works==0.3.4
-gunicorn==18.0
+gunicorn==19.5.0
 django-markup==0.4
 Pillow==8.2.0