Bump djangorestframework from 3.11.0 to 3.11.2 in /backend

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.11.0 to 3.11.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.11.0...3.11.2)

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

Author: dependabot[bot]

backend/requirements.txt

@@ -7,7 +7,7 @@ ffmpeg-python==0.1.17
 subliminal==2.1.0
 gunicorn==19.9.0
 django-cors-headers==3.0.2
-djangorestframework==3.11.0
+djangorestframework==3.11.2
 django-rest-auth==0.9.5
 django-allauth==0.42.0
 django-rest-auth[with_social]