Chart.js number format

Put tooltips in ‘option’ like this:

options: {
  tooltips: {
      callbacks: {
          label: function(tooltipItem, data) {
              return tooltipItem.yLabel.toFixed(2).replace(/\d(?=(\d{3})+\.)/g, '$&,');
          }
      }
  }
}

Reference from https://github.com/chartjs/Chart.js/pull/160.