Updated Readme to fix DesiredCapabilities link 
Updated Readme to fix DesiredCapabilities link 

Fixing this issue https://github.com/facebook/php-webdriver/issues/283
OndraM/php-webdriver,cedricalfonsi/php-webdriver,OndraM/php-webdriver,cedricalfonsi/php-webdriver,OndraM/php-webdriver,OndraM/php-webdriver