title: Highcharts: Custom button - symbol is misplaced
body: <p>I have added a new custom button, with my own symbol image:
  But the image is not placed as should :(
  Can some one help?
  Thanks
  Chanan</p>
  
  <p><img src="https://i.stack.imgur.com/NXbm8.png" alt="enter image description here"></p>
  
  <p>Here is how i added the button:</p>
  
  <pre><code>    exporting: {
          buttons: {
              'myButton': {
                  _id: 'myButton',
                  symbol: 'url(images/gallery/reset_zoom.jpg)',
                  x: -62,
                  symbolFill: '#B5C9DF',
                  hoverSymbolFill: '#779ABF',
                  onclick: function() {
                      alert('click!')
                  }
              }
          }
      }
  </code></pre>