Update v0.24.0.txt

Author: harisbal

doc/source/whatsnew/v0.24.0.txt

@@ -218,7 +218,7 @@ For earlier versions this can be done using the following.
 .. ipython:: python
 
    pd.merge(left.reset_index(), right.reset_index(),
-            on=['key'], how='inner').set_index(['key','X','Y'])
+            on=['key'], how='inner').set_index(['key', 'X', 'Y'])
 
 .. _whatsnew_0240.enhancements.rename_axis: