DOC: update the pandas.DataFrame.apply docstring

Author: mdeboc

pandas/core/frame.py

@@ -4821,7 +4821,7 @@ def apply(self, func, axis=0, broadcast=None, raw=False, reduce=None,
         """
         Apply a function along an axis of the DataFrame.
 
-        Objects passed to the function are Series objects having as index
+        Objects passed to the function are Series objects whose index is
         either the DataFrame's index (``axis=0``)
         or the DataFrame's columns (``axis=1``).
         If ``result_type is None``, the final return type is the return