Update pytest-runner to 6.0.0

[pyup-bot]

This PR updates pytest-runner from 5.3.1 to 6.0.0.

Changelog

6.0.0

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* 49: Dropped workaround for older setuptools versions.
* Require Python 3.7.

5.3.2

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* 58: Fixed syntax issue in changelog.

Links

• PyPI: https://pypi.org/project/pytest-runner
• Changelog: https://pyup.io/changelogs/pytest-runner/
• Repo: https://github.com/pytest-dev/pytest-runner/

[coveralls]

Coverage remained the same at 86.413% when pulling 6e90c10 on pyup-update-pytest-runner-5.3.1-to-6.0.0 into 2716a32 on master.