Make db_constraint unflagging backward compatible

Author: macro1

simple_history/models.py

@@ -220,8 +220,8 @@ def get_history_user(self, instance):
 class CustomForeignKeyField(models.ForeignKey):
 
     def __init__(self, *args, **kwargs):
-        kwargs['db_constraint'] = False
         super(CustomForeignKeyField, self).__init__(*args, **kwargs)
+        self.db_constraint = False
         self.generate_reverse_relation = False
 
     def get_attname(self):