Bump phpunit/phpunit from 5.7.19 to 5.7.27

Bumps [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) from 5.7.19 to 5.7.27.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/5.7.27/ChangeLog-5.7.md)
- [Commits](sebastianbergmann/phpunit@5.7.19...5.7.27)

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