Bump djangorestframework from 3.9.0 to 3.9.1 (#2)

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.9.0 to 3.9.1.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.9.0...3.9.1)

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

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

requirements.txt

@@ -4,7 +4,7 @@ defusedxml==0.5.0
 Django==2.2.13
 django-filter==2.0.0
 django-rest-auth==0.9.3
-djangorestframework==3.9.0
+djangorestframework==3.9.1
 idna==2.7
 Markdown==3.0.1
 oauthlib==2.1.0