Bump django from 1.8.14 to 2.2.28

Bumps [django](https://github.com/django/django) from 1.8.14 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.8.14...2.2.28)

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

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

requirements.txt

@@ -1,4 +1,4 @@
-Django==1.8.14
+Django==2.2.28
 pytz==2015.4
 wsgiref==0.1.2
 djangorestframework==3.1.3