In RSPEC Practice 3 it says:
Bonus: Refactor your `String#caesar` method to work with strings containing both upper- and lowercase letters.
Does this mean that all of the Uppercase letters stay Uppercase (e.g. “Z” shift 3 would equal “C”) or does this mean that the new letter will depend on their ASCII code (e.g. if I had an uppercase “Z” and a shift of 3, it would change into a lower case “c”)?