Bump pytest from 5.1.2 to 5.1.3

Bumps [pytest](https://github.com/pytest-dev/pytest) from 5.1.2 to 5.1.3.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](https://github.com/pytest-dev/pytest/compare/5.1.2...5.1.3)

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

requirements-dev.txt

@@ -1,7 +1,7 @@
 -e .
 flake8==3.7.8
 async-timeout==3.0.1
-pytest==5.1.2
+pytest==5.1.3
 pytest-cov==2.7.1
 pytest-mock==1.10.4
 coverage==4.5.4