More work on fix for #424 - TypeError: can't pickle _thread.lock objects.

AWS and Mongo brockers should be pickeled correctly now.

django_q/brokers/mongo.py

@@ -19,6 +19,10 @@ class Mongo(Broker):
         super(Mongo, self).__init__(list_key)
         self.collection = self.get_collection()
 
+    def __setstate__(self, state):
+        super(Mongo, self).__setstate__(state)
+        self.collection = self.get_collection()
+
     @staticmethod
     def get_connection(list_key: str = Conf.PREFIX) -> MongoClient:
         return MongoClient(**Conf.MONGO)