ios 原生Tabbar去掉顶部横线，顶部圆角效果

Swift版
tabBar.backgroundImage = UIImage.init()
tabBar.shadowImage = UIImage.init()

tabBar.layer.cornerRadius = 16
tabBar.layer.maskedCorners = [.layerMinXMinYCorner, .layerMaxXMinYCorner]

Oc版
//添加顶部圆角
self.view.layer.cornerRadius = 16;
self.view.layer.maskedCorners = kCALayerMinXMinYCorner | kCALayerMaxXMinYCorner;