Game Center Unity 5 Fix

extern "C" {
    void _ReportAchievementProgress(const char *achievementID, float progress, bool showsCompletionBanner) {

        GKAchievement *achievement = [[GKAchievement alloc] initWithIdentifier:[NSString stringWithUTF8String:achievementID]];
        achievement.percentComplete = progress;
        achievement.showsCompletionBanner = showsCompletionBanner;

        [GKAchievement reportAchievements:@[achievement] withCompletionHandler:^(NSError *error) {
            if(error != nil) {
                NSLog(@"Error reporting achievement: %@", error.localizedDescription);
            }
        }];
    }
}