Bump pytest from 4.5.0 to 4.6.1 (#102)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 4.5.0 to 4.6.1.
- [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/4.5.0...4.6.1)

requirements.dev.txt

@@ -2,5 +2,5 @@ flake8==3.7.7
 Cython==0.29.10
 nose==1.3.7
 pylint==1.9.4
-pytest==4.5.0
+pytest==4.6.1
 pytest-watch==4.2.0