title: rounded corners to a rectangle?
body: <p>Currently the legends of my chart that I generate in c3.js are rectangles of colors, I would like to change it by circles. how can I do it?</p>
  
  <p><a href="https://i.stack.imgur.com/NJRp3.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/NJRp3.png" alt="enter image description here"></a></p>
  
  <pre><code>var chart = c3.generate({
    data: {
        columns: [
            ['data1', 30],
            ['data2', 120],
        ],
        type : 'donut',
        onclick: function (d, i) { console.log("onclick", d, i); },
        onmouseover: function (d, i) { console.log("onmouseover", d, i); },
        onmouseout: function (d, i) { console.log("onmouseout", d, i); },
        label:true,
    },
    donut: {
        title: "Iris Petal Width",
         label: {
         /*format: function(value, ratio, id)
         {
           return d3.format('')(value)
         },*/
         show: false
        }
    }
  });
  </code></pre>
  
  <p><a href="http://plnkr.co/edit/JD52FXdZxEIcgP865w4h?p=preview" rel="nofollow noreferrer">Plunker</a></p>