Fix mixin inheritance.

Author: WaVEV

django_mongodb/fields/auto.py

@@ -6,7 +6,7 @@
 from .objectid_mixin import ObjectIdMixin
 
 
-class ObjectIdAutoField(AutoField, ObjectIdMixin):
+class ObjectIdAutoField(ObjectIdMixin, AutoField):
     def __init__(self, *args, **kwargs):
         kwargs["db_column"] = "_id"
         super().__init__(*args, **kwargs)

django_mongodb/fields/objectid.py

@@ -6,7 +6,7 @@
 from .objectid_mixin import ObjectIdMixin
 
 
-class ObjectIdField(Field, ObjectIdMixin):
+class ObjectIdField(ObjectIdMixin, Field):
     def get_internal_type(self):
         return "ObjectIdField"