Wait, I think my test code incorrect. I revised my testing code to check the `$?.to_i` instead of the returned value from `Process.kill`. Now it is clear that PhantomJS is returning an exit code of 66 on Windows. In Ubuntu, the exit status is 15 (matching the TERM signal code). I'm not exactly sure what this tells us but I still think that the best way to exit is to use the PhantomJS api directly via the existing websocket connection.