Add __init__ to types.MethodType (#1499)

stdlib/3/types.pyi

@@ -140,6 +140,7 @@ class MethodType:
     __func__ = ...  # type: _StaticFunctionType
     __self__ = ...  # type: object
     __name__ = ...  # type: str
+    def __init__(self, func: Callable, obj: object) -> None: ...
     def __call__(self, *args: Any, **kwargs: Any) -> Any: ...
 class BuiltinFunctionType:
     __self__ = ...  # type: Union[object, ModuleType]