code: function write (filename, content) {
    const json = JSON.stringify(content, (key, value) => value === undefined ? null : value)
    fs.writeFileSync(filename, json)
    return json
  }
docs: Write output data in file system
  @param  {String} filename Output file name
  @param  {Array}  content  List of contents
  @return {String}          Stringified list of contents