Add Generic Typing to Queue.PriorityQueue and Queue.LifoQueue in python 2 (#3036)

Author: JasonGilholme

stdlib/2/Queue.pyi

@@ -27,5 +27,5 @@ class Queue(Generic[_T]):
     def get(self, block: bool = ..., timeout: Optional[float] = ...) -> _T: ...
     def get_nowait(self) -> _T: ...
 
-class PriorityQueue(Queue): ...
-class LifoQueue(Queue): ...
+class PriorityQueue(Queue[_T]): ...
+class LifoQueue(Queue[_T]): ...