Given a common phrase, return false if any individual word in the phrase contains duplicate letters. Return true otherwise.
noDuplicateLetters("Fortune favours the bold.") ➞ true
noDuplicateLetters("You can lead a horse to water, but you can't make him drink.") ➞ true
noDuplicateLetters("Look before you leap.") ➞ false
// Duplicate letters in "Look" and "before".
noDuplicateLetters("An apple a day keeps the doctor away.") ➞ false
// Duplicate letters in "apple", "keeps", "doctor", and "away".
Letter matches are case-insensitive.