Bump django from 2.2.8 to 2.2.20

Bumps [django](https://github.com/django/django) from 2.2.8 to 2.2.20.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.8...2.2.20)

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

requirements.txt

@@ -1,4 +1,4 @@
-Django==2.2.8
+Django==2.2.20
 requests==2.22.0
 mock==3.0.5
 django-crispy-forms==1.7.2