  from django.contrib.gis.geometry.backend import Geometry, GeometryException
  from django.core.exceptions import ImproperlyConfigured
  from django.db.models.expressions import Expression
  from django.db.models.fields import Field
  from django.utils import six
  from django.utils.translation import ugettext_lazy as _
  
  # Local cache of the spatial_ref_sys table, which holds SRID data for each
  # spatial database alias. This cache exists so that the database isn't queried
  # for SRID info each time a distance query is constructed.
 
</s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six
 </s> add  </s> remove from django.utils import six, timezone
 </s> add from django.utils import timezone </s> remove from django.utils import six
 </s> add 
  from django.contrib.gis.geometry.backend import Geometry, GeometryException
  from django.core.exceptions import ImproperlyConfigured
  from django.db.models.expressions import Expression
  from django.db.models.fields import Field

  from django.utils.translation import ugettext_lazy as _
  
  # Local cache of the spatial_ref_sys table, which holds SRID data for each
  # spatial database alias. This cache exists so that the database isn't queried
  # for SRID info each time a distance query is constructed.
keep keep keep keep replace keep keep keep keep keep
 Refs #23919 -- Removed six.<various>_types usage

Thanks Tim Graham and Simon Charette for the reviews. 
django/contrib/gis/db/models/fields.py