code: function set(key, value) {
    let config = getGlobalConfig();
    if (key && typeof key === 'string' && typeof value !== 'undefined') {
      config = _.set(config, key, value);
    } else if (_.isObject(key)) {
      config = _.merge(config, key);
    } else if (typeof value !== 'undefined') {
      config = _.merge(config, value);
    }
    // update config meta
    config.meta = config.meta || {};
    config.meta.updated_at = Math.round(+new Date() / 1000);
    // write to .serverlessrc file
    writeFileAtomic.sync(serverlessrcPath, JSON.stringify(config, null, 2));
    return config;
  }
docs: set global .serverlessrc config value.