add duckOthers option on iOS

[EyadAlghamdi]

• I have added duckOthers option for iOS

• also updated the index.d.ts params here for setActive method. which was wrong

[denpy]

@zmxv hey, I was wondering if there is anything I can do to get this PR merged? Tested it, and it worked as expected.

[glaydsoncosta]

Any change this can be reviewed and merged?

[Will-Mann-16]

Heads up - we patched this into our repo, this causes a crash on Android. It was due to the number of arguments. A fix we did:

Sound.setCategory = function(value, mixWithOthers = false, duckOthers = false) {
  if (!IsWindows) {
    if(IsAndroid) {
      RNSound.setCategory(value, mixWithOthers);
    } else {
      RNSound.setCategory(value, mixWithOthers, duckOthers);
    }
  }
};