Update recommonmark to 0.7.1

[pyup-bot]

This PR updates recommonmark from 0.5.0 to 0.7.1.

Changelog

0.7.0

-------------

Date: 2020-12-17

-   [limasierra](https://github.com/limasierra): Bugfix: External links to 'supported' files 
 lose their file extension ([\181](https://github.com/readthedocs/recommonmark/pull/181))

Links

• PyPI: https://pypi.org/project/recommonmark
• Changelog: https://pyup.io/changelogs/recommonmark/
• Repo: https://github.com/rtfd/recommonmark