Bump django from 3.1.7 to 3.1.8

Bumps [django](https://github.com/django/django) from 3.1.7 to 3.1.8.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/3.1.7...3.1.8)

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

requirements.txt

@@ -1,5 +1,5 @@
 coverage==5.4
-Django==3.1.7
+Django==3.1.8
 django-appconf==1.0.4
 django-autoslug==1.9.8
 django-compressor==2.4