Update pytest-runner to 6.0.0

[pyup-bot]

This PR updates pytest-runner from 4.4 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.

5.1

===

* 49: Surgically restore support for older setuptools versions.

5.0

===

* 42: Prefer pyproject.toml
* Refresh package metadata.
* This release now intentionally introduces the changes
unintionally brought about in 4.5 and 4.3, where the
adoption of declarative config adds a new requirement
on setuptools 30.4 or later. On systems running older
setuptools, installation of pytest-runner via
``easy_install`` (or ``setup_requires``), will result
in a ``DistributionNotFound`` exception.

All projects should pin to ``pytest-runner < 5``
or upgrade the environment to ``setuptools >= 30.4``
(prior to invoking setup.py).

4.5.1

=====

* 48: Revert changes from 4.5 - restoring project to the
state at 4.4.

4.5

===

(Pulled from PyPI due to 43 and 48)

* Packaging (skeleton) refresh, including adoption of
`black <https://pypi.org/project/black>`_ for style.

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 #407