code: function getSvgHeight (svg, filename) {
    const parseSvg = /<svg[^>]+height\s*=\s*["']?(\d+)\s*(pt|px|)["']?/i.exec(svg);
    if (!parseSvg) {
      throw new Error(`could not read height for '${filename}'.`);
    }
    return parseSvg[1];
  }
docs: Reads the height of the svg
  
  @param  {String} svg      the svg content
  @param  {String} filename the file name for error reporting
  @return {Number}          height