code: function backup(source, options) {
    options = _.sanitize(options, {destination: null});
    let dest = options.destination;
    if (dest === null) {
      dest = `${source.replace(/\/*$/, '')}_${Date.now()}`;
    }
    copy(source, dest);
    return dest;
  }
docs: Backup a file or directory
  @function $file~backup
  @param {string} source
  @param {Object} [options]
  @param {Object} [options.destination] - Destination path to use when copying. By default, the backup will
  be placed in the same directory, adding a timestamp
  @returns {string} - The final destination
  @example
  // Backup a file (it will automatically append a timestamp to it: 'conf/my.cnf_1453811340')
  $file.backup('conf/my.cnf'});
  @example
  // Backup a file with a specific name and location 'conf/my.cnf.default'
  $file.backup('conf/my.cnf', {destination: 'conf/my.cnf.default'});