title: Pie chart with drilldown not working
body: <p><br />
  Here's a plunker:<br/>
  <a href="http://plnkr.co/edit/S1B9Q9e1yen0QgmKt2ri" rel="nofollow">http://plnkr.co/edit/S1B9Q9e1yen0QgmKt2ri</a></p>
  
  <pre><code>var chartConfig = {
    title: {
      text: 'Number of offers by trend'
    },
    subtitle: {
      text: 'My company'
    },
    plotOptions: {
      series: {
        dataLabels: {
          enabled: true,
          format: '{point.name}: {point.y:.1f}%'
        }
      }
    },
  
    tooltip: {
      headerFormat: '&lt;span style="font-size:11px"&gt;{series.name}&lt;/span&gt;&lt;br&gt;',
      pointFormat: '&lt;span style="color:{point.color}"&gt;{point.name}&lt;/span&gt;: &lt;b&gt;{point.y:.2f}%&lt;/b&gt; of total&lt;br/&gt;'
    },
    options: {
      chart: {
        type: 'pie'
      },
      legend: {
        align: 'right',
        x: -70,
        verticalAlign: 'top',
        y: 20,
        floating: true,
        backgroundColor: (Highcharts.theme &amp;&amp; Highcharts.theme.background2) || 'white',
        borderColor: '#CCC',
        borderWidth: 1,
        shadow: false
      },
      tooltip: {
        headerFormat: '&lt;span style="font-size:11px"&gt;{series.name}&lt;/span&gt;&lt;br&gt;',
        pointFormat: '&lt;span style="color:{point.color}"&gt;{point.name}&lt;/span&gt;: &lt;b&gt;{point.y:.2f}%&lt;/b&gt; of total&lt;br/&gt;'
      },
      plotOptions: {
        column: {
          stacking: 'normal',
          dataLabels: {
            enabled: true,
            color: (Highcharts.theme &amp;&amp; Highcharts.theme.dataLabelsColor) || 'white',
            style: {
              textShadow: '0 0 3px black, 0 0 3px black'
            }
          }
        }
      }
    },
    series: [{
      name: 'Trends',
      colorByPoint: true,
      data: TREND_LIST
    }],
    drilldown: {
      series: NUMBER_OF_OFFERS_BY_TREND
    }
  };
  </code></pre>
  
  <p>the pie is drown fine but I can't click to get the drill down pie</p>
  
  <p>And this is the original fiddle from highcharts.com, I changed it a bit so it can work with highcharts-ng:<br />
  bit.ly/1kOPi7L</p>
  
  <p>Thanks for helping</p>