-Updated ExoPlayer to r2.5.1.

-Fixes some more deprecations due to Exoplayer and Android O notification updates.

app/src/main/java/org/schabi/newpipe/player/MainVideoPlayer.java

@@ -422,6 +422,11 @@ public class MainVideoPlayer extends Activity {
         public ImageButton getPlayPauseButton() {
             return playPauseButton;
         }
+
+        @Override
+        public void onRepeatModeChanged(int i) {
+
+        }
     }
 
     private class MySimpleOnGestureListener extends GestureDetector.SimpleOnGestureListener implements View.OnTouchListener {