`django_redis` failing to import `six` from `django.utils`

Traceback:

```

Internal Server Error: /harem/reponse/
Traceback (most recent call last):
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/core/cache/__init__.py", line 50, in _create_cache
    backend_cls = import_string(backend)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/utils/module_loading.py", line 17, in import_string
    module = import_module(module_path)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django_redis/cache.py", line 8, in <module>
    from .util import load_class
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django_redis/util.py", line 8, in <module>
    from django.utils import six
ImportError: cannot import name 'six'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/core/handlers/exception.py", line 34, in inner
    response = get_response(request)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/utils/deprecation.py", line 93, in __call__
    response = self.process_request(request)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/contrib/sessions/middleware.py", line 20, in process_request
    request.session = self.SessionStore(session_key)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/contrib/sessions/backends/cache.py", line 17, in __init__
    self._cache = caches[settings.SESSION_CACHE_ALIAS]
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/core/cache/__init__.py", line 79, in __getitem__
    cache = _create_cache(alias)
  File "/home/yangcoco/.virtualenvs/Django_czbk/lib/python3.6/site-packages/django/core/cache/__init__.py", line 53, in _create_cache
    "Could not find backend '%s': %s" % (backend, e))
django.core.cache.backends.base.InvalidCacheBackendError: Could not find backend 'django_redis.cache.RedisCache': cannot import name 'six'

```

Using:
`django-redis 4.10.0`
`python 3.6`