Update phpunit/phpunit requirement from ^4.5|^5 to ^4.5|^5|^6 (#9)
Update phpunit/phpunit requirement from ^4.5|^5 to ^4.5|^5|^6 (#9)

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/6.5.0/ChangeLog-6.5.md)
- [Commits](https://github.com/sebastianbergmann/phpunit/commits/6.5.0)

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

Co-authored-by: dependabot-preview[bot] <6a4c1c4838f800d1998274cd5234e1f65c55e90c@users.noreply.github.com>
akovalyov/DebugStatementsFixers