update demo to Android SDK v4.13

Author: oliverou

README.md

@@ -8,7 +8,7 @@ This sample code demonstrates how to use [FFmpeg](https://ffmpeg.org) for video
 
  - Android Studio 2.0+
  - Android System 4.2+
- - DJI Android SDK 4.11.1
+ - DJI Android SDK 4.13
 
 ## IMPORTANT: Install `git lfs`