code: function getOldestFilename (callback) {
    getLogFiles(function (err, files) {
      if (err) {
        callback(err, null);
      } else if (!files || files.length === 0) {
        return callback(null, Date.now().toString().concat(FILE_EXT));
      } else {
        var file = _.min(files, function (f) {
          // Remove extension to get just the timestamp
          var ts = f.name.replace(FILE_EXT, '');
  
          return parseInt(ts, 10);
        });
  
        callback(null, file.name);
      }
    });
  }
docs: Get the name of the most recent log file
  @param  {Array}    files
  @param  {Function} callback