去除tableview 在plain下，组标题悬浮状态

原理就是进行偏移放到navigationBar底部

- (void)scrollViewDidScroll:(UIScrollView *)scrollView {
    CGFloat sectionHeaderHeight = kPixToRealH(48);
    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);
    }
}