Bump pytest from 4.2.0 to 4.2.1 (#73)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 4.2.0 to 4.2.1.
- [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/4.2.0...4.2.1

)

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