title: Change ChartJs axis title dynamically
body: <p>I've created a chart like this</p>
  
  <pre><code>if (userLanguageCode === "es") {
      customTooltipFormat = 'DD/MM/YYYY, HH:mm:ss';
  
      customDisplayFormats = {
          'millisecond': 'SSS [ms]',
          'second': 'HH:mm:ss', // 11:20:01 AM
          'minute': 'D/MM/YY HH:mm', // 11:20:01 AM
          'hour': 'D/MM/YY HH[h]', // Sept 4, 5PM
          'day': 'D/MM/YYYY', // Sep 4 2015
          'week': 'll', // Week 46, or maybe "[W]WW - YYYY" ?
          'month': 'MMM YYYY', // Sept 2015
          'quarter': '[Q]Q - YYYY', // Q3
          'year': 'YYYY', // 2015
      };
  }
  
  Chart.defaults.global.responsive = true;
  Chart.defaults.global.animation = false;
  
  datosChartHistoricos =  {
      labels: [],
      datasets: [{
          label: textoValor,
          backgroundColor: "rgba(0,181,255,0.5)",
          fill: chartWithIncrementValues? true: false,
          borderColor: "rgba(0,192,192,1)",
          pointBorderColor: "rgba(0,181,255,1)",
          pointBackgroundColor: "rgba(255,255,255,1)",
          pointBorderWidth: 1,
          data: []
      }]
  };
  
  var ctx = document.getElementById("grafica").getContext("2d");
  chartHistoricos = new Chart(ctx, {
      type: chartWithIncrementValues? "bar" : "line",
      data: datosChartHistoricos,
      options: {
          responsive: true,
          elements: {
              rectangle: {
                  borderWidth: 1,
                  borderColor: 'rgb(0, 0, 0)',
                  borderSkipped: 'bottom'
              }
          },
          scales: {
              xAxes: [{
                  type: "time",
                  time: {
                      tooltipFormat: customTooltipFormat,
                      displayFormats: customDisplayFormats,
                  }
              }, ],
              yAxes: [{
                  scaleLabel: {
                      display: true,
                      labelString: textoValor + " (" + unidadesValor + ")"
                  }
              }]
          },
          legend: {
              display: false,
          }
      }
  });
  </code></pre>
  
  <p>This is the default config for the chart, data is added dynamically, but the user can choose different data values to show, like temperature, distance... To do this, I just change the data value of the dataset and the label, but I can't figure how to change the yAxis label using javascript when I change the dataset value. Initialization title is ok.</p>
  
  <p>Any tips?</p>
  
  <p>Thanks!</p>