DOC: Series.mask() should point to Series.where() and vice versa
In the docs page of `pandas.Series.mask()`, the _See also_ cell that should point to related methods (at least in my understanding) is linking to `pandas.DataFrame.where()` instead of `pandas.Series.where()`
(See [here](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.Series.mask.html) for the latest doc page).  
The same issue appears in the doc page of  `pandas.Series.where()` where `pandas.DataFrame.mask()` is linked.

Following the logic of the doc pages of `pandas.DataFrame.where()/.mask()`, where the two methods link each other, I assume that `pandas.Series.mask()` should link to `pandas.Series.where()` and vice versa.

I offer to take care of this small issue if it is substantial.

This is still there in 0.24.devX at the time of writing. 0.23.3 is the current stable release.
