Bump pytest from 5.0.1 to 5.1.0

Bumps [pytest](https://github.com/pytest-dev/pytest) from 5.0.1 to 5.1.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@5.0.1...5.1.0)

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

requirements.txt

@@ -1,4 +1,4 @@
-pytest==5.0.1
+pytest==5.1.0
 pytest-cov
 pytest-pep8
 pytest-travis-fold