function addRectToResize(svgString, viewBox) {
  const addrect = `<rect width="${viewBox.width}" height="${viewBox.height}" id="delete-me"/></svg>`;
  return NSString.stringWithString(svgString.replace('</svg>', addrect));
}
@name addRectToResize
@description add rect to keep proportion on resize
@param svgString
@param viewBox
@returns {String}