!19646 修改媒体播放实例代码错误

Merge pull request !19646 from FULIZHONG/0614flz

zh-cn/application-dev/reference/apis/js-apis-media.md

@@ -1071,7 +1071,7 @@ getCurrentTrack(trackType: MediaType, callback: AsyncCallback\<number>): void
 let mediaType = media.MediaType.MEDIA_TYPE_AUD;
 let trackIndex = null;
 
-avPlayer.getCurrentTrack(mediaType  (err, index) => {
+avPlayer.getCurrentTrack(mediaType, (err, index) => {
   if (err == null) {
     console.info('getCurrentTrack success');
     trackIndex = index;