chore(deps-dev): bump guzzlehttp/guzzle in /vendor-bin/php-coveralls

Bumps [guzzlehttp/guzzle](https://github.com/guzzle/guzzle) from 7.12.0 to 7.13.1.
- [Release notes](https://github.com/guzzle/guzzle/releases)
- [Changelog](https://github.com/guzzle/guzzle/blob/7.13/CHANGELOG.md)
- [Commits](guzzle/guzzle@7.12.0...7.13.1)

---
updated-dependencies:
- dependency-name: guzzlehttp/guzzle
  dependency-version: 7.12.1
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]