ios11坑

1.UITableView，UICollectionView 顶部20像素

解决办法：

if(@available(iOS11.0, *)) {

        UIScrollView.appearance.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;

    }else{

        self.automaticallyAdjustsScrollViewInsets = NO;

   }