Run migrations check only if required version of django is installed
Run migrations check only if required version of django is installed

Django master changed the `max_length` of `AbstractUser`'s `first_name`.

See
- https://github.com/django/django/commit/5f8495a40ab1554e81ac845484da890dd390e1d8
- https://github.com/django-guardian/django-guardian/commit/88b8d41ada5de7db2452d67e28955332bf48ecf8

lukaszb/django-guardian,lukaszb/django-guardian,lukaszb/django-guardian