message: Change YYYY to yyyy for date-fns 2.0.0-alpha.16
  See for context.
  There is a subtle difference between the two around January 1st, which breaks the YearSelection component and possibly other things.
  yyyy is now the correct format to use.
diff: @@ -188,11 +188,11 @@ export default class DateFnsUtils {
  // displaying methpds
  getCalendarHeaderText(date) {
  - return format(date, 'MMMM YYYY', { locale: this.locale });
  + return format(date, 'MMMM yyyy', { locale: this.locale });
  }
  getYearText(date) {
  - return format(date, 'YYYY', { locale: this.locale });
  + return format(date, 'yyyy', { locale: this.locale });
  }
  getDatePickerHeaderText(date) {
  