Bump guzzlehttp/guzzle from 7.5.1 to 7.6.0 (#13)

Bumps [guzzlehttp/guzzle](https://github.com/guzzle/guzzle) from 7.5.1 to 7.6.0.
- [Release notes](https://github.com/guzzle/guzzle/releases)
- [Changelog](https://github.com/guzzle/guzzle/blob/7.6/CHANGELOG.md)
- [Commits](guzzle/guzzle@7.5.1...7.6.0)

---
updated-dependencies:
- dependency-name: guzzlehttp/guzzle
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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