Bump django from 2.2.6 to 2.2.8

Bumps [django](https://github.com/django/django) from 2.2.6 to 2.2.8.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2.6...2.2.8)

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

requirements.txt

@@ -8,7 +8,7 @@ cffi==1.13.1
 chardet==3.0.4
 coverage==4.5.4
 cryptography==2.8
-Django==2.2.6
+Django==2.2.8
 django-appconf==1.0.3
 django-autoslug==1.9.6
 django-compressor==2.3