Update pytest-runner to 6.0.0

[pyup-bot]

This PR updates pytest-runner from 5.1 to 6.0.0.

Changelog

6.0.0

======

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

5.3.2

======

* 58: Fixed syntax issue in changelog.

5.3.1

======

* Refreshed package metadata.

5.3.0

======

* Require Python 3.6 or later.
* Refreshed package metadata.

5.2

===

* 50: This project is deprecated.

Links

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

[pyup-bot]

Closing this in favor of #445