Bump django from 3.0.9 to 3.1

Bumps [django](https://github.com/django/django) from 3.0.9 to 3.1.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.0.9...3.1)

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

requirements.txt

@@ -2,7 +2,7 @@ whitenoise==3.3.1
 gunicorn==20.0.4
 dj-database-url==0.5.0
 psycopg2==2.8.5
-Django==3.0.9
+Django==3.1
 beautifulsoup4==4.9.1
 requests==2.24.0
 markdown==3.2.2