Pin pytest-runner to latest version 3.0

[pyup-bot]

pytest-runner is not pinned to a specific version.

I'm pinning it to the latest version 3.0 for now.

These links might come in handy: PyPI | Changelog | Repo

Changelog

3.0

• Dropped support for Python 2.6 and 3.1.

2.12.2

• 33: Packaging refresh.

2.12.1

• 32: Fix support for dependency_links.

2.12

• 30: Rework support for --allow-hosts and
  --index-url, removing dependence on
  setuptools.Distribution's private member.
  Additionally corrects logic in marker evaluation
  along with unit tests!

2.11.1

• 28: Fix logic in marker evaluation.

2.11

• 27: Improved wording in the README around configuration
  for the distutils command and pytest proper.

2.10.1

• 21: Avoid mutating dictionary keys during iteration.

2.10

• 20: Leverage technique in setuptools 794 <https://github.com/pypa/setuptools/issues/794>_
  to populate PYTHONPATH during test runs such that
  Python subprocesses will have a dependency context
  comparable to the test runner.

2.9

• Added Trove Classifier indicating this package is part
  of the pytest framework.

2.8

• 16: Added a license file, required for membership to
  pytest-dev.
• Releases are now made automatically by pushing a
  tagged release that passes tests on Python 3.5.

2.7

• Moved hosting to Github.

2.6

• Add support for un-named, environment-specific extras.

2.5.1

• Restore Python 2.6 compatibility.

2.5

• Moved hosting to pytest-dev <https://bitbucket.org/pytest-dev/pytest-runner>_.

2.4

• Added documentation <https://pythonhosted.org/pytest-runner>_.
• Use setuptools_scm for version management and file discovery.
• Updated internal packaging technique. README is now included
  in the package metadata.

2.3

• Use hgdistver for version management and file discovery.

2.2

• Honor .eggs directory for transient downloads as introduced in Setuptools
  7.0.

2.1

• The preferred invocation is now the 'pytest' command.

2.0

• Removed support for the alternate usage. The recommended usage (as a
  distutils command) is now the only supported usage.
• Removed support for the --junitxml parameter to the ptr command. Clients
  should pass the same parameter (and all other py.test arguments) to py.test
  via the --addopts parameter.

1.1

• Added support for --addopts to pass any arguments through to py.test.
• Deprecated support for --junitxml. Use --addopts instead. --junitxml will be
  removed in 2.0.

1.0

Initial implementation.

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖