Bump djangorestframework from 3.10.1 to 3.11.2 in /docs/_ext/djangodummy

Bumps [djangorestframework](https://github.com/encode/django-rest-framework) from 3.10.1 to 3.11.2.
- [Release notes](https://github.com/encode/django-rest-framework/releases)
- [Commits](encode/django-rest-framework@3.10.1...3.11.2)

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

docs/_ext/djangodummy/requirements.txt

@@ -1,5 +1,5 @@
 # for readthedocs
 # Remaining requirements are picked up from setup.py
 Django==2.2.13
-djangorestframework==3.10.1
+djangorestframework==3.11.2
 sphinxcontrib-django == 0.4