Updated version of xlrd broke the application's ability to handle .xlsx files.

[jonespm]

@jonespm, looks like the bump to 2.0.1 for xlrd broke the application's ability to handle .xlsx files. I dunno exactly what to do about this.

See the release notes about not supporting .xlsx: https://pypi.org/project/xlrd/
This appears to be an alternative that could also replace .xlwt: https://openpyxl.readthedocs.io/en/stable/

Originally posted by @ssciolla in #255 (comment)

[jonespm]

It was decided to just leave it updated and only support xls files for now. We may want to revisit and switch this module in the future.