增大 button 的可点击范围，之所以写了两种，是因为第二种有可能会被其他重写或者 oc category 给覆盖掉。

EnlargeButton.swift

class EnlargeButton: UIButton {
    override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        return bounds.insetBy(dx: -20, dy: -20).contains(point)
    }
}

extension UIButton {
    open override func point(inside point: CGPoint, with event: UIEvent?) -> Bool {
        return bounds.insetBy(dx: -20, dy: -20).contains(point)
    }
}