Updated the stub for builtins to change slice to take Optional[int] rather than just straight int.

Author: froomzy

stdlib/3/builtins.pyi

@@ -472,7 +472,7 @@ class slice:
     start = 0
     step = 0
     stop = 0
-    def __init__(self, start: int, stop: int = 0, step: int = 0) -> None: ...
+    def __init__(self, start: Optional[int], stop: Optional[int] = 0, step: Optional[int] = 0) -> None: ...
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
     def __init__(self, iterable: Iterable[_T_co] = ...) -> None: ...