title: Change button background image in swift
body: <p>I am programming a dice app.
  I know how to change the image to different dice faces if I use UIImage view. But I want to use a UIButton for dice so that every time a user presses the dice button with a particular dice face image, the image updates to another dice image. I know how to use the arc4random to randomly change the image but I don't know how to apply that same concept on a UIButton.</p>