Fix typo

stdlib/2/os/__init__.pyi

@@ -194,7 +194,7 @@ def unlink(path: _PathType) -> None: ...
 def utime(path: _PathType, times: Optional[Tuple[int, int]]) -> None: ...
 def walk(top: AnyStr, topdown: bool = ..., onerror: Any = ...,
          followlinks: bool = ...) -> Iterator[Tuple[AnyStr, List[AnyStr],
-                                                    List[Anystr]]]: ...
+                                                    List[AnyStr]]]: ...
 
 def abort() -> None: ...
 def execl(file: _PathType, *args) -> None: ...