Bar now only returns a discount during happy hour. Updates:
Added happy_hour attr_writer to Bar
Wrote a happy_hour? method that takes Time.now.hour and checks if it's happy hour (3:00pm to 4:00pm)
Updated the happy_discount method to return the happy hour discount during happy hour and to return 0 outside of happy hour
Stubbed Time.now at 2:00pm to test happy_hour method
Bar constrains its happy hour discount between zero and one (adds onto happy_discount method to check for happy_discount value).

Bar knows when it's happy hour (uses Time.stub(:now).and_return(happy_hour))
Bar knows if it is not happy hour otherwise (Set the happy_hour? method to check if Time.now.hour is between 15 and 16 o'clock)