Bump phpro/grumphp from 1.15.0 to 1.16.0 (#509)

Bumps [phpro/grumphp](https://github.com/phpro/grumphp) from 1.15.0 to 1.16.0.
- [Release notes](https://github.com/phpro/grumphp/releases)
- [Commits](phpro/grumphp@v1.15.0...v1.16.0)

---
updated-dependencies:
- dependency-name: phpro/grumphp
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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