Bump django from 2.2.6 to 2.2.28

Bumps [django](https://github.com/django/django) from 2.2.6 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.6...2.2.28)

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

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

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@ defusedxml==0.6.0
 diff-match-patch==20181111
 #psycopg2>=2.7,<3.0
 #psycopg2-binary
-Django==2.2.6
+Django==2.2.28
 django-cors-headers==3.1.1
 django-filter==2.2.0
 django-import-export==1.2.0