retina-logo.html

<a href="{{ shop.url }}">
  <img 
    src="{{ 'logo.png' | asset_url }}" 
    alt="{{ shop.name }}" 
    data-retina-src="{{ 'logo.svg' | asset_url }}">
</a>
<script type="text/javascript">
  Modernizr.addTest('retina', function () {
    return (!!navigator.userAgent.match(/Macintosh|Mac|iPhone|iPad/i) && window.devicePixelRatio==2);
  });
  Modernizr.load([
    {
      test : Modernizr.retina,
      yep : '{{ "jquery-retinadisplay.js" | asset_url }}', // https://github.com/gavroche/jquery-retinadisplay
      complete : function () {
        if(Modernizr.retina) {
          $('img[data-retina-src]').retinaDisplay();
        }
      }
    }
  ]);
</script>