Update idna to 3.1

[pyup-bot]

This PR updates idna from 2.10 to 3.1.

Changelog

3.1

++++++++++++++++

- Ensure license is included in package (Thanks, Julien Schueller)
- No longer mark wheel has universal (Thanks, Matthieu Darbois)
- Test on PowerPC using Travis CI

3.0

++++++++++++++++

- Python 2 is no longer supported (the 2.x branch supports Python 2,
use "idna<3" in your requirements file if you need Python 2 support)
- Support for V2 UTS 46 test vectors.

Links

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