message: add flow to helpers.js
diff: -const normalize = (fields) => {
  +// @flow
  +
  +const normalize = (fields: Array<any> | Object): Object => {
  if (Array.isArray(fields)) {
  return fields.reduce((prev, curr) => {
  if (~curr.indexOf('.')) {
  @@ -16,10 +18,8 @@ const normalize = (fields) => {
  /**
  * Maps fields to computed functions.
  - *
  - * @param {Array|Object} fields
  */
  -const mapFields = (fields) => {
  +const mapFields = (fields: Array<any> | Object): Object => {
  const normalized = normalize(fields);
  return Object.keys(normalized).reduce((prev, curr) => {
  const field = normalized[curr];
  