Laravel Elixir BrowserSync Proxy not Working

I've just installed Laravel 5.3, it's a completely fresh install and after looking through the Docs i've set up my Gulpfile as follows:

elixir((mix) => {
    mix.sass('app.scss')
       .webpack('app.js')
       .version(['css/app.css', 'js/app.js'])
       .browserSync({
         proxy: 'subdomain.mydomain.dev'
       });
});

For some reason every single time i run gulp watch it launches the browser towards localhost:3000

What am i doing wrong? Isn't this supposed to direct the BrowserSync to my Mamp Vhost if i set the address exactly the same?