Problem 4

Write a function that creates an object with each (key, value) pair being the (lower case, upper case) versions of a letter, respectively.

All the letters in the input list will always be lowercase.

mapping(["p", "s"]) // { "p": "P", "s": "S" }

mapping(["a", "b", "c"]) // { "a": "A", "b": "B", "c": "C" }

mapping(["a", "v", "y", "z"]) // { "a": "A", "v": "V", "y": "Y", "z": "Z" }