Bump django from 2.2 to 2.2.28

Bumps [django](https://github.com/django/django) from 2.2 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2...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

@@ -9,7 +9,7 @@ chardet==3.0.4
 defusedxml==0.6.0
 diff-match-patch==20181111
 dj-database-url==0.5.0
-Django==2.2
+Django==2.2.28
 django-allauth==0.39.1
 django-cors-headers==3.4.0
 django-countries==5.3.3