Updating php-webdriver to latest version

This latest version provides a fix for a breaking change in Selenium's WireProtocol

* New specs: https://code.google.com/p/selenium/wiki/JsonWireProtocol#/session
* Change in Selenium: https://code.google.com/p/selenium/source/detail?r=8c3c65772d57
* Relevant update in php-webdriver: https://github.com/instaclick/php-webdriver/commit/10dcea308e5cf4c182c8fd0ca7f8381aefc4a416