Update django requirement from ~=3.0 to ~=3.1
Update django requirement from ~=3.0 to ~=3.1

Updates the requirements on [django](https://github.com/django/django) to permit the latest version.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/3.0...3.1)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
petervanderdoes/wger,wger-project/wger,rolandgeider/wger,wger-project/wger,rolandgeider/wger,petervanderdoes/wger,wger-project/wger,rolandgeider/wger,rolandgeider/wger,petervanderdoes/wger,wger-project/wger,petervanderdoes/wger