Bump react/http-client from 0.5.6 to 0.5.9

Bumps [react/http-client](https://github.com/reactphp/http-client) from 0.5.6 to 0.5.9.
- [Release notes](https://github.com/reactphp/http-client/releases)
- [Changelog](https://github.com/reactphp/http-client/blob/master/CHANGELOG.md)
- [Commits](reactphp/http-client@v0.5.6...v0.5.9)

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Author: dependabot-support