use phantomjs-prebuilt (#3704)

Author: Shyam-Chen

docs/browser-setup.md

@@ -131,7 +131,7 @@ capabilities: {
    * Can be used to specify the phantomjs binary path.
    * This can generally be ommitted if you installed phantomjs globally.
    */
-  'phantomjs.binary.path': require('phantomjs').path,
+  'phantomjs.binary.path': require('phantomjs-prebuilt').path,
 
   /*
    * Command line args to pass to ghostdriver, phantomjs's browser driver.