docs: function updatePacks(packs) {
    var didUpdate = false;
    var updated = packs.map(function(pack) {
      var mtime_ = readMTime(pack.id);
      if (pack.mtime !== mtime_) {
        didUpdate = true;
        return {
          id: pack.id,
          source: readFile(pack.id),
          mtime: mtime_
        };
      } else {
        return pack;
      }
    });
    return didUpdate ? updated : packs;
  }