docs: function getId(rootFolder) {
      return new Promise((resolve, reject) => {
          const dir = path.join(rootFolder, constants.META_DIR, constants.META_ID);
          fs.readFile(dir, 'utf8', (err, id) => {
              if (err) {
                  reject(err);
                  return;
              } else {
                  resolve(id);
                  return;
              }
          });
      });
  }