lib/google_holiday_calendar/calendar.rb
def holiday?(arg)
      date = to_date(arg)
      holidays(start_date: date, end_date: date + 1.day, limit: 1).length > 0
    end
def holiday?(arg)
      date = to_date(arg)
      holidays(start_date: date, end_date: date + 1.day, limit: 1).length > 0
    end
whether arg is holiday
 @param arg [#to_date, String] {Date}, {Time}, or date like String (ex. "YYYY-MM-DD")