Django 3 support

[pyprism]

Does this package support django 3.0 ? Recently I upgraded my project from django 2.x to 3.0.
When I tried to run manage.py command it throws this error :

 File "/../.env/lib/python3.7/site-packages/silk/models.py", line 21, in <module>
    from silk.config import SilkyConfig
  File "/../.env/lib/python3.7/site-packages/silk/config.py", line 3, in <module>
    from django.utils import six
ImportError: cannot import name 'six' from 'django.utils' (/../.env/lib/python3.7/site-packages/django/utils/__init__.py)

[knyghty]

This is being addressed in #380

[nasirhjafri]

Added in #385 and #380

[nasirhjafri]

Added in release 4.0.0 (#384)