UITableView设置系统cell的分割线顶头

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath{
    cell.layoutMargins = UIEdgeInsetsZero;
    cell.separatorInset = UIEdgeInsetsZero;
    cell.preservesSuperviewLayoutMargins = NO;
}