解决iOS 11 下 UICollectionView 的HeaderView 遮挡滚动条

实现即可

- (void)collectionView:(UICollectionView *)collectionView willDisplaySupplementaryView:(UICollectionReusableView *)view forElementKind:(NSString *)elementKind atIndexPath:(NSIndexPath *)indexPath {

    view.layer.zPosition = 0.0;

}