Update idna to 2.8

[pyup-bot]

This PR updates idna from 2.6 to 2.8.

Changelog

2.8

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

- Update to Unicode 11.0.0.
- Provide more specific exceptions for some malformed labels.

2.7

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

- Update to Unicode 10.0.0.
- No longer accepts dot-prefixed domains (e.g. ".example") as valid.
This is to be more conformant with the UTS 46 spec. Users should
strip dot prefixes from domains before processing.

Links

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

[codecov-io]

Codecov Report

Merging #65 into master will not change coverage.
The diff coverage is n/a.

@@         Coverage Diff          @@
##           master   #65   +/-   ##
====================================
  Coverage      30%   30%           
====================================
  Files           3     3           
  Lines          10    10           
====================================
  Hits            3     3           
  Misses          7     7

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[pyup-bot]

Closing this in favor of #161