Change requirements to accept older Django versions.
Change requirements to accept older Django versions.

Note that development should still favor the latest release of Django.

korfuri/django-prometheus,wangwanzhong/django-prometheus,korfuri/django-prometheus,wangwanzhong/django-prometheus,DingaGa/django-prometheus,obytes/django-prometheus,DingaGa/django-prometheus,obytes/django-prometheus