Bump pytest from 5.1.2 to 5.3.2 (#178)

Bumps [pytest](https://github.com/pytest-dev/pytest) from 5.1.2 to 5.3.2.
- [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...5.3.2

)

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