Remove object as the only ancestor for string.Formatter in Python 3 stubs. (#1072)

stdlib/3/string.pyi

@@ -25,7 +25,7 @@ class Template:
                         **kwds: str) -> str: ...
 
 # TODO(MichalPokorny): This is probably badly and/or loosely typed.
-class Formatter(object):
+class Formatter:
     def format(self, format_string: str, *args: Any, **kwargs: Any) -> str: ...
     def vformat(self, format_string: str, args: Sequence[Any],
                 kwargs: Mapping[str, Any]) -> str: ...