Bump django from 2.2.20 to 2.2.21

Bumps [django](https://github.com/django/django) from 2.2.20 to 2.2.21.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.20...2.2.21)

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

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

requirements.txt

@@ -8,7 +8,7 @@ certifi==2020.11.8
 chardet==3.0.4
 decorator==4.4.2
 defusedxml==0.6.0
-Django==2.2.20
+Django==2.2.21
 entrypoints==0.3
 idna==2.8
 importlib-metadata==2.0.0