Update pip-tools to 3.1.0

[pyup-bot]

This PR updates pip-tools from 2.0.2 to 3.1.0.

Changelog

### 3.1.0 ``` Features: - Added support of `pip` 18.1 ([689](https://github.com/jazzband/pip-tools/pull/689)). Thanks vphilippon ``` ### 3.0.0 ``` Major changes: - Update `pip-tools` for native `pip` 8, 9, 10 and 18 compatibility, un-vendoring `pip` to use the user-installed `pip` ([657](https://github.com/jazzband/pip-tools/pull/657) and [672](https://github.com/jazzband/pip-tools/pull/672)). Thanks to techalchemy, suutari, tysonclugg and vphilippon for contributing on this. Features: - Removed the dependency on the external library `first` ([676](https://github.com/jazzband/pip-tools/pull/676)). Thanks jdufresne ```

Links

- PyPI: https://pypi.org/project/pip-tools - Changelog: https://pyup.io/changelogs/pip-tools/ - Repo: https://github.com/jazzband/pip-tools/

[coveralls]

Pull Request Test Coverage Report for Build 714

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.07%) to 97.889%

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Files with Coverage Reduction	New Missed Lines	%
astrality/module.py	3	97.38%
<!--	Total:	3		-->

Totals
Change from base Build 553:	-0.07%
Covered Lines:	4405
Relevant Lines:	4500

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💛 - Coveralls