message: add flow typings for date utils
diff: import { parse, isValid, format as formatDate } from 'date-fns';
  +// @flow
  +
  /**
  * Custom parse behavior on top of date-fns parse function.
  - * @param {String} date
  - * @param {String} format
  - * @return {Date|null}
  */
  -export const parseDate = (date, format) => {
  +export function parseDate (date: string, format: string): ?Date {
  const parsed = parse(date, format, new Date());
  // if date is not valid or the formatted output after parsing does not match
  