Bump pytest from 3.9.3 to 3.10.0

Bumps [pytest](https://github.com/pytest-dev/pytest) from 3.9.3 to 3.10.0.
- [Release notes](https://github.com/pytest-dev/pytest/releases)
- [Changelog](https://github.com/pytest-dev/pytest/blob/master/CHANGELOG.rst)
- [Commits](pytest-dev/pytest@3.9.3...3.10.0)

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

dev-requirements.txt

@@ -2,7 +2,7 @@
 invoke==1.2.0
 
 # Testing
-pytest==3.9.3
+pytest==3.10.0
 tox==3.5.3
 
 # Syntax checking