title: Chart.js - 2 does not display Axes labels
body: <p>i am trying to plot a line graph using vue-chartjs and Chart.js (2.7.1).
  the graph is displayed, but there are no xAxes and yAxes labels.</p>
  <p>This is my options object:</p>
  <pre><code>title: {
      display: true,
      text: 'Title',
  },
  responsive: true,
  maintainAspectRatio: false,
  elements: {
      line: {
          fill: false
      }        
  },
  scales: {
      xAxes: {
          scaleLabel: {
              display: true,
              labelString: 'LabelX',
          }
      },
      yAxes: {
          scaleLabel: {
              display: true,
              labelString: 'LabelY',
          }
      },
  }
  </code></pre>
  <p>I think that <strong>scales.xAxes.scaleLabel</strong> don't working.</p>