⬆️ Bump gunicorn from 20.1.0 to 21.2.0 (#99)

Bumps [gunicorn](https://github.com/benoitc/gunicorn) from 20.1.0 to 21.2.0.
- [Release notes](https://github.com/benoitc/gunicorn/releases)
- [Commits](benoitc/gunicorn@20.1.0...21.2.0)

---
updated-dependencies:
- dependency-name: gunicorn
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

docker-images/requirements.txt

@@ -1,2 +1,2 @@
 meinheld==1.0.2
-gunicorn==20.1.0
+gunicorn==21.2.0