Bump djangorestframework from 3.8.2 to 3.11.2

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.8.2 to 3.11.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](https://github.com/encode/django-rest-framework/compare/3.8.2...3.11.2)

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

requirements.txt

@@ -8,7 +8,7 @@ dask==0.20.0
 decorator==4.3.0
 Django==2.0.7
 django-rest-framework==0.1.0
-djangorestframework==3.8.2
+djangorestframework==3.11.2
 gast==0.2.0
 grpcio==1.16.0
 gunicorn==19.9.0