Bump djangorestframework from 3.0.0 to 3.11.2

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.0.0 to 3.11.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.0.0...3.11.2)

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

requirements.txt

@@ -3,7 +3,7 @@ dj-database-url==0.3.0
 dj-static==0.0.6
 django-appconf==0.6
 django-compressor==1.4
-djangorestframework==3.0.0
+djangorestframework==3.11.2
 drf-nested-routers==0.9.0
 gunicorn==19.1.1
 six==1.8.0