Changes magic sequence to '!#mojo ' and strips 'mojo ' when building url

examples/js/world.js

-#!mojo:js_content_handler
+#!mojo mojo:js_content_handler
 // See hello.js.
 define("main", [
   "console",
   "mojo/services/public/js/application",
 ], function(console, application) {
 
   var Application = application.Application;
 
   class World extends Application {
     initialize(args) {
       console.log(this.url + ": World");
       this.quit();
     }
   }
 
   return World;
 });