Merge pull request #31 from CaiJingLong/fix-video-badge

fix video badge

lib/src/delegate/badge_delegate.dart

   @override
   Widget buildBadge(BuildContext context, AssetType type, Duration duration) {
     if (type == AssetType.video) {
-      var s = duration.inSeconds;
-      var m = duration.inMinutes;
+      var s = duration.inSeconds % 60;
+      var m = duration.inMinutes % 60;
       var h = duration.inHours;
 
       String text =