Change Queue.put return type to Future[None]

stdlib/3.4/asyncio/queues.pyi

@@ -29,7 +29,7 @@ class Queue(Generic[T]):
     def empty(self) -> bool: ...
     def full(self) -> bool: ...
     @coroutine
-    def put(self, item: T) -> Future: ...
+    def put(self, item: T) -> Future[None]: ...
     def put_nowait(self, item: T) -> None: ...
     @coroutine
     def get(self) -> Future[T]: ...