update mobile demo

docs/assets/js/mobile.js

@@ -2,7 +2,7 @@ var vConsole = new VConsole();
 
 var art = new Artplayer({
     container: '.artplayer-app',
-    url: '/assets/sample/video.mp4',
+    url: 'https://artplayer.org/assets/sample/video.mp4',
     title: 'One More Time One More Chance',
     poster: '/assets/sample/poster.jpg',
     autoSize: true,