update doc

Author: auderson

doc/source/whatsnew/v1.5.0.rst

@@ -599,7 +599,7 @@ Groupby/resample/rolling
 - Bug in :meth:`GroupBy.cummax` with ``int64`` dtype with leading value being the smallest possible int64 (:issue:`46382`)
 - Bug in :meth:`GroupBy.max` with empty groups and ``uint64`` dtype incorrectly raising ``RuntimeError`` (:issue:`46408`)
 - Bug in :meth:`.GroupBy.apply` would fail when ``func`` was a string and args or kwargs were supplied (:issue:`46479`)
--
+- Bug in :meth:`Rolling.skew` and :meth:`Rolling.kurt` would give NaN with window of same values (:issue:`30993`)
 
 Reshaping
 ^^^^^^^^^