Bump facebook/webdriver from 1.6.0 to 1.7.1

Bumps [facebook/webdriver](https://github.com/facebook/php-webdriver) from 1.6.0 to 1.7.1.
- [Release notes](https://github.com/facebook/php-webdriver/releases)
- [Changelog](https://github.com/facebook/php-webdriver/blob/community/CHANGELOG.md)
- [Commits](https://github.com/facebook/php-webdriver/compare/1.6.0...1.7.1

)

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