Update idna to 2.7

[pyup-bot]

This PR updates idna from 2.6 to 2.7.

Changelog

### 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

[coveralls]

Pull Request Test Coverage Report for Build 532

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 97.784%

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Totals
Change from base Build 505:	0.0%
Covered Lines:	4369
Relevant Lines:	4468

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💛 - Coveralls