Update behat/behat requirement in /build/integration

Updates the requirements on [behat/behat](https://github.com/Behat/Behat) to permit the latest version.
- [Release notes](https://github.com/Behat/Behat/releases)
- [Changelog](https://github.com/Behat/Behat/blob/master/CHANGELOG.md)
- [Commits](https://github.com/Behat/Behat/compare/v3.5.0...v3.6.1

)

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