Ambiguous description in pandas.DataFrame.to_parquet documentation
#### Relevant Docstring

In the verson 0.22.0 [pandas.DataFrame.to_parquet documentation](https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_parquet.html), the **engine** kwarg is described as:
>"Parquet reader library to use. If ‘auto’, then the option ‘io.parquet.engine’ is used. If ‘auto’, then the first library to be installed is used."

The two descriptions of "auto" are in conflict, so the one that isn't correct should be removed.
