Odin Project Ruby Ceaser Cipher

ceaser_cipher.rb

def caesar_cipher(message, shift)
	split_message = message.split("").map do |letter|
		# If letter is not an alphabet do not change it
		if letter.downcase.ord < 97 or letter.downcase.ord > 128
			letter
		else
			code = letter.ord + shift
			if (letter == letter.upcase && code > 90) || (letter == letter.downcase && code > 122)
				code -= 26
			end
			code.chr
		end
	end
	return split_message.join("")
end

puts caesar_cipher("What a string!", 5)