Bump django from 1.11.29 to 2.2.28

Bumps [django](https://github.com/django/django) from 1.11.29 to 2.2.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.11.29...2.2.28)

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

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

requirements.txt

@@ -1,5 +1,5 @@
 #Django<1.11.0
-Django==1.11.29
+Django==2.2.28
 django-extensions==1.9.8
 git+https://github.com/dbca-wa/ledger#egg=ledger
 # last stable commit for ledger tagged v2021.03.05.03 pr#836