Correction to whatsnew. Reference index level instead of index (GH 14327)

Author: Jon M. Mease

doc/source/whatsnew/v0.19.1.txt

@@ -46,4 +46,4 @@ Bug Fixes
 - Bug in ``pd.concat`` where names of the ``keys`` were not propagated to the resulting ``MultiIndex`` (:issue:`14252`)
 - Bug in ``MultiIndex.set_levels`` where illegal level values were still set after raising an error (:issue:`13754`)
 - Bug in ``DataFrame.to_json`` where ``lines=True`` and a value contained a ``}`` character (:issue:`14391`)
-- Bug in ``df.groupby`` causing an ``AttributeError`` when grouping a single index frame by a column and the index (:issue`14327`)
+- Bug in ``df.groupby`` causing an ``AttributeError`` when grouping a single index frame by a column and the index level (:issue`14327`)