switch to six.python_2_unicode_compatible

Author: johanneswilm

binary_database_files/models.py

@@ -4,7 +4,7 @@
 from django.conf import settings
 from django.db import models
 from django.utils import timezone
-from django.utils.encoding import python_2_unicode_compatible
+from six import python_2_unicode_compatible
 
 from django.db.models import BinaryField