Bump pytest from 5.4.2 to 5.4.3 (#200)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 5.4.2 to 5.4.3.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@5.4.2...5.4.3)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

requirements_dev.txt

@@ -6,7 +6,7 @@ executor >= 21.0
 click >=7.0,<8.0
 
 # Unit tests.
-pytest ==5.4.2
+pytest ==5.4.3
 pytest-cov == 2.10.0
 pypng == 0.0.20