去除UITableView SectionHeader的粘性

- (void)scrollViewDidScroll:(UIScrollView *)scrollView
{
    CGFloat sectionHeaderHeight = 40;
    if (scrollView.contentOffset.y <= sectionHeaderHeight && scrollView.contentOffset.y >= 0) {
        scrollView.contentInset = UIEdgeInsetsMake(-scrollView.contentOffset.y, 0, 0, 0);
    }
    else if (scrollView.contentOffset.y >= sectionHeaderHeight) {
        scrollView.contentInset = UIEdgeInsetsMake(-sectionHeaderHeight, 0, 0, 0);
    }
}