Update videojs-vtt-thumbnails to latest upstream version

Note that the latest version on NPM is over two years old so this was built from source.

assets/js/player.js

@@ -149,7 +149,8 @@ if (!video_data.params.listen && video_data.params.quality === 'dash') {
 }
 
 player.vttThumbnails({
-    src: location.origin + '/api/v1/storyboards/' + video_data.id + '?height=90'
+    src: location.origin + '/api/v1/storyboards/' + video_data.id + '?height=90',
+    showTimestamp: true
 });
 
 // Enable annotations