Bump pytest from 4.2.0 to 4.2.1

Bumps [pytest](https://github.com/pytest-dev/pytest) from 4.2.0 to 4.2.1.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@4.2.0...4.2.1)

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

requirements_dev.txt

@@ -11,7 +11,7 @@ Sphinx==1.8.4
 twine==1.12.1
 pylint==2.2.2
 
-pytest==4.2.0
+pytest==4.2.1
 pytest-runner==4.2
 pytest-cov==2.6.1