title: Property 'yAxis' does not exist on type 'ExportingButtonsOptionsObject'
body: <p>I am using highcharts-angular and typescript and trying to update y-axis type but getting error</p>
  <blockquote>
  <p>Property 'yAxis' does not exist on type 'ExportingButtonsOptionsObject'</p>
  </blockquote>
  <p>This is the code and getting error on</p>
  <pre><code>onclick: function () {
              this.yAxis[0].update({
                type: 'linear'
              })
            }
  </code></pre>
  <p>Whole code:</p>
  <pre><code>yAxis: [
        {
          labels: {
              align: 'left'
          },
          height: '80%',
          resize: {
              enabled: true
          }
        }, 
        {
          labels: {
              align: 'left'
          },
          top: '80%',
          height: '20%',
          offset: 0
        }
      ],
      exporting: {
        buttons: {
          contextButton: {
            enabled: false,
            align: 'left',
          },
          customButton: {
            text: 'Linear',
            onclick: function () {
              this.yAxis[0].update({
                type: 'linear'
              })
            }
          },
          customButton2: {
            text: 'Logarithmic',
            onclick: function () {
              this.yAxis[0].update({
                type: 'logarithmic'
              })
            }
          }
        }
      },
  </code></pre>