Bump guzzlehttp/guzzle from 6.5.3 to 6.5.4

Bumps [guzzlehttp/guzzle](https://github.com/guzzle/guzzle) from 6.5.3 to 6.5.4.
- [Release notes](https://github.com/guzzle/guzzle/releases)
- [Changelog](https://github.com/guzzle/guzzle/blob/6.5.4/CHANGELOG.md)
- [Commits](guzzle/guzzle@6.5.3...6.5.4)

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