Write a function that finds the word "bomb" in the given string (not case sensitive). Return "DUCK!" if found, otherwise,"Relax, there's no bomb.".
bomb("There is a bomb.") ➞ "DUCK!"
bomb("Hey, did you think there is a BOMB?") ➞ "DUCK!"
bomb("This goes boom!!!") ➞ "Relax, there's no bomb.""bomb" may appear in different character cases (i.e. uppercase, lowercase, mixed).