Upgrade black version (#7089)

stdlib/@python2/SocketServer.pyi

@@ -50,6 +50,7 @@ if sys.platform != "win32":
             RequestHandlerClass: Callable[..., BaseRequestHandler],
             bind_and_activate: bool = ...,
         ) -> None: ...
+
     class UnixDatagramServer(BaseServer):
         def __init__(
             self,