/**
  * Return the id of a leaderboard (category or identifier, depending on iOS version)
  *
  * @param leaderboard
  * @return
  */
 public String getLeaderboardId(GKLeaderboard leaderboard) {
   if (getIosVersion() >= IOS_7) {
     return leaderboard.getIdentifier();
   } else {
     return leaderboard.getCategory();
   }
 }