Bump pytest-runner from 4.2 to 4.4

Bumps [pytest-runner](https://github.com/pytest-dev/pytest-runner) from 4.2 to 4.4.
- [Release notes](https://github.com/pytest-dev/pytest-runner/releases)
- [Changelog](https://github.com/pytest-dev/pytest-runner/blob/master/docs/history.rst)
- [Commits](pytest-dev/pytest-runner@4.2...4.4)

Signed-off-by: dependabot[bot] <support@dependabot.com>

requirements.txt

@@ -9,7 +9,7 @@ Sphinx==1.8.1
 twine==1.12.1
 
 pytest==3.8.2
-pytest-runner==4.2
+pytest-runner==4.4
 
 # Self dependency! Nice way to get tool updates...
 python-dev-tools