Bump djangorestframework from 3.14.0 to 3.15.2

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.14.0 to 3.15.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.14.0...3.15.2)

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

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

requirements.txt

@@ -11,7 +11,7 @@ django-tables2==2.5.2
 #### Python PostgreSQL library
 psycopg2-binary==2.9.6
 #### Django REST API libraries
-djangorestframework==3.14.0
+djangorestframework==3.15.2
 django-cors-headers==3.13.0
 #### Python & Django Elasticsearch libraries
 elasticsearch==7.17.9