fix: Django 3.0 deprecation import fix

[igor-yamshchykov]

According to Django 3 release
both django.utils.six and django.contrib.staticfiles.templatetags.staticfiles.static() are removed

This PR should fix ImportErrors

[v1kku]

I think the it should try to import from the new location first then fallback to the old one. Doing it the other way round will still raise warnings.

e.g

try:
    from django.templatetags.static import static
except ImportError:
    from django.contrib.staticfiles.templatetags import static

There's also another static import in tests/tests.py and a few others for six.

[igor-yamshchykov]

@v1kku thanks, added

[domdinicola]

I think we should get rid of things which are not supported anymore (like six)

[domdinicola]

#266 hope this fixes it

[Gagaro]

Django 1.11 is still supported so we should keep using six for the moment.

Thanks for the PR 👍 .