uitableview disable sticky header
let dummyViewHeight = CGFloat(40)
self.tableView.tableHeaderView = UIView(frame: CGRect(x: 0, y: 0, width: self.tableView.bounds.size.width, height: dummyViewHeight))
self.tableView.contentInset = UIEdgeInsets(top: -dummyViewHeight, left: 0, bottom: 0, right: 0)