itemgetter parameters can be any type that the container accepts, not just int (#564)

Author: gjcarneiro

stdlib/2and3/operator.pyi

@@ -161,9 +161,9 @@ def attrgetter(attr: str) -> Callable[[Any], Any]: ...
 def attrgetter(*attrs: str) -> Callable[[Any], Tuple[Any, ...]]: ...
 
 @overload
-def itemgetter(item: int) -> Callable[[Any], Any]: ...
+def itemgetter(item: Any) -> Callable[[Any], Any]: ...
 @overload
-def itemgetter(*items: int) -> Callable[[Any], Tuple[Any, ...]]: ...
+def itemgetter(*items: Any) -> Callable[[Any], Tuple[Any, ...]]: ...
 
 def methodcaller(name: str, *args: Any, **kwargs: Any) -> Callable[..., Any]: ...