fix loc to accept Index as arg (#63)

Author: Dr-Irv

pandas/core/frame.pyi

@@ -64,6 +64,8 @@ class _LocIndexerFrame(_LocIndexer):
     def __getitem__(self, idx: Tuple[Union[IndexType, MaskType], StrLike],) -> Series[Dtype]: ...    
     @overload
     def __getitem__(self, idx: Tuple[Union[IndexType, MaskType], Union[List[StrLike], slice]],) -> DataFrame: ...    
+    @overload
+    def __getitem__(self, idx: Index) -> DataFrame: ...
 
     def __setitem__(
         self,