Upgrade black version (#7089)

stdlib/@python2/mmap.pyi

@@ -30,6 +30,7 @@ class mmap(Sequence[bytes]):
         def __init__(
             self, fileno: int, length: int, flags: int = ..., prot: int = ..., access: int = ..., offset: int = ...
         ) -> None: ...
+
     def close(self) -> None: ...
     def flush(self, offset: int = ..., size: int = ...) -> int: ...
     def move(self, dest: int, src: int, count: int) -> None: ...