Changed iteritems() to items() in fetch_all_worker_data()

The size of the list would still be changing while iterating over the dictionary as worker creation is now asynchronous. items() creates a copy of the dictionary, which I think we should use for now. Note that items() in python 3 changes to an iterator.

aimmo-game/simulation/worker_managers/worker_manager.py

@@ -39,7 +39,8 @@ def get_code(self, player_id):
         return self._data.get_code(player_id)
 
     def fetch_all_worker_data(self, player_id_to_game_state):
-        for player_id, worker in self.player_id_to_worker.iteritems():
+        # Work with the current copy of the list, as the size of the dictionary is changing
+        for player_id, worker in self.player_id_to_worker.items():
             worker.fetch_data(player_id_to_game_state[player_id])
 
     def get_player_id_to_serialised_actions(self):