Bump django from 2.2 to 2.2.13

Bumps [django](https://github.com/django/django) from 2.2 to 2.2.13.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2...2.2.13)
Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

 asgiref==3.2.10
 attrs==20.2.0
 coverage==5.2.1
-Django==2.2
+Django==2.2.13
 djangorestframework==3.11.1
 iniconfig==1.0.1
 more-itertools==8.5.0