Bump django from 3.0.7 to 3.1.12 in /server

Bumps [django](https://github.com/django/django) from 3.0.7 to 3.1.12.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@3.0.7...3.1.12)

---
updated-dependencies:
- dependency-name: django
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

server/requirements.txt

@@ -7,7 +7,7 @@ chardet==3.0.4
 cloudinary==1.21.1
 colour==0.1.5
 dj-database-url==0.5.0
-Django==3.0.7
+Django==3.1.12
 django-appconf==1.0.4
 django-cloudinary-storage==0.2.3
 django-colorfield==0.3.1