Bump djangorestframework from 3.14.0 to 3.15.1

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.14.0 to 3.15.1.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.14.0...3.15.1)

---
updated-dependencies:
- dependency-name: djangorestframework
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements.txt

@@ -5,7 +5,7 @@ django-debug-toolbar
 django-debug-toolbar-force
 django-environ==0.11.2
 django-extensions==3.2.3
-djangorestframework==3.14.0
+djangorestframework==3.15.1
 djangorestframework-camel-case==1.4.2
 docutils==0.20.1
 drf-yasg[validation]==1.21.7