⬆️ Bump gevent from 20.9.0 to 21.1.2 in /backend/uclapi (#3125)

Bumps [gevent](https://github.com/gevent/gevent) from 20.9.0 to 21.1.2.
- [Release notes](https://github.com/gevent/gevent/releases)
- [Changelog](https://github.com/gevent/gevent/blob/master/docs/changelog_pre.rst)
- [Commits](gevent/gevent@20.9.0...21.1.2)

Signed-off-by: dependabot[bot] <support@github.com>

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

backend/uclapi/requirements.txt

@@ -15,7 +15,7 @@ django-postgrespool2==1.0.1
 eventlet==0.30.0
 freezegun==1.1.0
 flake8==3.8.4
-gevent==20.9.0
+gevent==21.1.2
 gunicorn==20.0.4
 greenlet==1.0.0
 hiredis==1.1.0