code: function getPath(image, s, wantsRetina) {
    if (s === 0) { return image.src; }
  
    var parts = image.src.split('.');
    var ext = parts.pop();
  
    return parts.join('.') + '-' + s + (wantsRetina ? '@2x' : '') + '.' + ext;
  }
docs: Get the path for the image given the current breakpoints and
  browser features.
  @param {ResponsiveImage} image The image data.
  @param {String} s Requested path.
  @param {boolean} wantsRetina If we should look for retina.
  @return {String} The resulting path.