Fixed issue with sending special keys

Right now there is a bug in the dalek-internal-actions repo (https://github.com/dalekjs/dalek-internal-actions/issues/1) about special keys not working.  The reason the special key are not working is because they use UTF-8 characters in order to send them.  Looking through the selenium's webdriver code, it seems like they send all requests with a method of POST or PUT with UTF-8 encoding so I have updated the driver's generateRequestOptions() method to do the same.