Python 2 fix.

Author: noamkush

rest_framework/fields.py

@@ -903,7 +903,7 @@ def to_internal_value(self, data):
 
 # Number types...
 
-class MaxMinMixin:
+class MaxMinMixin(object):
     default_error_messages = {
         'max_value': _('Ensure this value is less than or equal to {max_value}.'),
         'min_value': _('Ensure this value is greater than or equal to {min_value}.'),