Eliminated the skipna / dropna inconsistency in the docs.


As @bf mentioned in the comments under the  issue #34063 ,
There are errors in the docs for Dataframe.mode, https://pandas.pydata.org/pandasdocs/dev/reference/api/pandas.DataFrame.mode.html (See source : https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L8722-L8807) , where the dropna parameter (which occurs more number of times than skipna) has been named skipna (first occurrence on line 8370).  