title: C3.js piechart tooltip not showing
body: <p>i am trying to implement pie chart in my application but piechart tooltip not showing on mouseover</p>
  
  <p>below is my code</p>
  
  <pre><code>&lt;link rel="icon"  href="https://cdnjs.cloudflare.com/ajax/libs/c3/0.6.2/c3.min.css"&gt;
  
  &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/d3/4.13.0/d3.min.js"&gt;&lt;/script&gt;
  &lt;script src="https://cdnjs.cloudflare.com/ajax/libs/c3/0.6.2/c3.min.js" &gt;&lt;/script&gt;
  
  
  &lt;div id="chart"&gt;&lt;/div&gt;
  
  &lt;script&gt;
  var chart = c3.generate({
      bindto:'#chart',
      data: {
          columns: [
              ['data1', 30],
              ['data2', 50]
          ],
          type: 'pie'
      },
      pie: {
          label: {
              format: function (value, ratio, id) {
                  return value;
              }
          }
      },
        tooltip: {
        format: {
            title: function (d) { return 'Data ' + d; },
            value: function (value, ratio, id) {
                    return value;
            }
  //            value: d3.format(',') // apply this format to both y and y2
        }
    },
  });
  &lt;/script&gt;
  </code></pre>
  
  <p>i have created fiddle for the same,below is the url</p>
  
  <p><a href="https://jsfiddle.net/alokranjan39/sf9xL7m4/3/" rel="nofollow noreferrer">https://jsfiddle.net/alokranjan39/sf9xL7m4/3/</a></p>