Changed CONTIBUTING.md link to a relative link
Changed CONTIBUTING.md link to a relative link

cartland/android-UniversalMusicPlayer,eneim/android-UniversalMusicPlayer,MaTriXy/android-UniversalMusicPlayer,android/uamp,android/uamp,bright-sparks/android-UniversalMusicPlayer,xCatG/android-UniversalMusicPlayer