disambiguate documentation for pandas.Series replace
Currently, the `pandas.Series` that is used for the example for `pandas.Series.replace` has an index which is identical to its values (i.e. `pandas.Series([0, 1, 2, 3, 4])`). This can be quite confusing at a first glance (as it was for me), as I assumed that `pandas.Series.replace` was using the index of the series (whereas it is actually using the values). Updated the documentation to use `pandas.Series([1, 2, 3, 4, 5])` to remove this ambiguity.
