UITableView下移20PX

    //声明tableView的位置 添加下面代码
    if (@available(iOS 11.0, *)) {
        self.userCenterTab.contentInsetAdjustmentBehavior = UIScrollViewContentInsetAdjustmentNever;
    } else {
        self.automaticallyAdjustsScrollViewInsets = NO;
    }