Bump djangorestframework from 3.12.4 to 3.15.2

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.12.4 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.12.4...3.15.2)

---
updated-dependencies:
- dependency-name: djangorestframework
  dependency-type: direct:production
...

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

requirements.txt

@@ -49,7 +49,7 @@ django-jsonfield==1.4.1
 django-modeltranslation==0.12.2
 django-nose==1.4.5
 django-oauth-toolkit==2.1.0
-djangorestframework==3.12.4
+djangorestframework==3.15.2
 django-robots==4.0
 django-security==0.12.0
 django-storages[google]==1.14.3