Create a function that takes a string and returns the first character that repeats. If there is no repeat of a character, return "0".
firstRepeat("legolas") ➞ "l"
firstRepeat("Gandalf") ➞ "a"
firstRepeat("Balrog") ➞ "0"
firstRepeat("Isildur") ➞ "0"
// Case sensitive "I" not equal to "i"Tests are case sensitive.