Create a function that alternates the case of the letters in a string (known as Spongecase).
alternatingCaps("Hello") ➞ "HeLlO"
alternatingCaps("How are you?") ➞ "HoW aRe YoU?"
alternatingCaps("OMG this website is awesome!") ➞ "OmG tHiS wEbSiTe Is AwEsOmE!"