Bump php-coveralls/php-coveralls from 2.7.0 to 2.8.0 (#629)

Bumps [php-coveralls/php-coveralls](https://github.com/php-coveralls/php-coveralls) from 2.7.0 to 2.8.0.
- [Release notes](https://github.com/php-coveralls/php-coveralls/releases)
- [Changelog](https://github.com/php-coveralls/php-coveralls/blob/master/CHANGELOG.md)
- [Commits](php-coveralls/php-coveralls@v2.7.0...v2.8.0)

---
updated-dependencies:
- dependency-name: php-coveralls/php-coveralls
  dependency-version: 2.8.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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Author: dependabot[bot]