title: Flutter CircleAvatar backgroundImage not filling up the circle
body: <p>I am using a <a href="https://docs.flutter.io/flutter/material/CircleAvatar-class.html" rel="noreferrer">CircleAvatar</a> with a <code>backgroundImage</code> property to load an image took from a camera but the image shown does not fill the entire circle avatar. It looks like a rectangular image in a circle. </p>
  
  <p>How do I make the image expand to cover the circle avatar? Thanks.</p>