Chart.js Doughnut - multiple dataset

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.7.2/Chart.bundle.min.js"></script>
<div id="deviceChartCont">
<canvas id="deviceChart"></canvas>
</div>

JavaScript

var platform_labels = ["Tablet","Ordenador"];
  var platform_dataset = [14,5];
  var os_labels = ["Android","Windows","GNU\/Linux"];
  var os_dataset = [14,4,1];
  var devices_labels = ["Tablet","Ordenador","Android","Windows","GNU\/Linux"];
  
  
      var chartColors = {
          red: 'rgb(255, 99, 132)',
          orange: 'rgb(255, 159, 64)',
          yellow: 'rgb(255, 205, 86)',
          green: 'rgb(75, 192, 192)',
          blue: 'rgb(54, 162, 235)',
          purple: 'rgb(153, 102, 255)',
          grey: 'rgb(201, 203, 207)'
      };


      var config = {
          type: 'doughnut',
          data: {
              datasets: [{
                  data: platform_dataset,
                  backgroundColor: [
                      chartColors.red,
                      chartColors.orange,
                      chartColors.yellow
                  ],
                  label: 'Platform',
                  labels: platform_labels
              }, {
                  data: os_dataset,
                  backgroundColor: [
                      chartColors.purple,
                      chartColors.green,
                      chartColors.blue
                  ],
                  label: 'OS',
                  labels: os_labels
              }],
              labels: devices_labels
          },
          options: {
              tooltips: {
                  callbacks: {
                      label: function (tooltipItem, data) {
                          var dataset = data.datasets[tooltipItem.datasetIndex];
                          var index = tooltipItem.index;
                          return dataset.labels[index] + ": " + dataset.data[index];
                      }
                  }
              }
          }
      };
      var ctx = document.getElementById('deviceChart').getContext('2d');
      var employeesGraph = new Chart(ctx, config);