Add six imports for Django master compatibility

Implement forwards compatibility for missing
django.utils.six package imports on Django 2.2

Relates to django-compressor/django-appconf#44
and can be removed after django-appconf
has received a new release which deprecates
the use of the integrated Django six library

Signed-off-by: Aleksi Häkli <aleksi.hakli@iki.fi>

axes/conf.py

@@ -1,3 +1,13 @@
+# TODO: Remove these imports after django-appconf does not depend on django.utils.six
+try:
+    from django.utils import six  # noqa
+except ImportError:  # pragma: no cover
+    import sys
+    import warnings
+
+    sys.modules['django.utils.six'] = __import__('six')
+    warnings.warn('django.utils.six was patched for django-appconf backwards compatibility', ImportWarning)
+
 from django.conf import settings
 from django.utils.translation import gettext_lazy as _
 

setup.py

@@ -34,10 +34,11 @@ setup(
     package_dir={'axes': 'axes'},
     python_requires='~=3.5',
     install_requires=[
-        'pytz',
         'django',
         'django-appconf',
         'django-ipware>=2.0.2',
+        'pytz',
+        'six',
     ],
     include_package_data=True,
     packages=find_packages(),