Enable mobileFallbackImage option for better eyecatch in mobile

Author: yasulab

img/why-coderdojo-wall-1.jpg

@@ -147,7 +147,7 @@
 	<div class="overlay"></div>
       </div>
 
-      <div id="youtube_video_player" class="player" data-property="{videoURL:'{{ site.eye_catch_video }}',containment:'#header_youtube',startAt:0,mute:true,autoPlay:true,loop:true,useOnMobile:true,opacity:1}"></div>
+      <div id="youtube_video_player" class="player" data-property="{videoURL:'{{ site.eye_catch_video }}',containment:'#header_youtube',startAt:0,mute:true,autoPlay:true,loop:true,useOnMobile:true,mobileFallbackImage:'/img/why-coderdojo-wall.webp',opacity:1}"></div>
 
       <!-- NOTE: Moved to the end of of 'top'. -->
       <div id="header">