chore(deps): 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-base.txt

@@ -6,7 +6,7 @@ django-generic-api-permissions==0.2.0
 django-localized-fields==6.7
 django-postgres-extra==2.0.8
 django-tree-queries==0.19.0
-djangorestframework==3.14.0
+djangorestframework==3.15.1
 djangorestframework-jsonapi==6.1.0
 mozilla-django-oidc==3.0.0
 pyexcel==0.7.0