Bump django from 2.2.18 to 2.2.28 (#83)

Bumps [django](https://github.com/django/django) from 2.2.18 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.18...2.2.28)

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

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requirements.txt

@@ -1,4 +1,4 @@
-Django==2.2.18
+Django==2.2.28
 djangorestframework==3.11.2
 django-cors-headers==3.7.0
 drf-tracking==1.5.0