Update phpunit/phpunit requirement from ^4.8 to ^5.7
Update phpunit/phpunit requirement from ^4.8 to ^5.7

Updates the requirements on [phpunit/phpunit](https://github.com/sebastianbergmann/phpunit) to permit the latest version.
- [Release notes](https://github.com/sebastianbergmann/phpunit/releases)
- [Changelog](https://github.com/sebastianbergmann/phpunit/blob/5.7.27/ChangeLog-5.7.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/compare/4.8.0...5.7.27)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
antonmarin/traceable-pdo