static getMinimumDaysInFirstWeek({ locale = null, locObj = null } = {}) {
    return (locObj || Locale.create(locale)).getMinDaysInFirstWeek();
  }
Get the minimum number of days necessary in a week before it is considered part of the next year according
to the given locale.
@param {Object} opts - options
@param {string} [opts.locale] - the locale code
@param {string} [opts.locObj=null] - an existing locale object to use
@returns {number}