input: Write a python function to reverse each word in a given string.
  assert reverse_words("emocleW ot gnirtS ecnerefxeT") == "Welcome to String Reference"
  assert reverse_words("sI si nuf") == "Is is fun"
output: def reverse_words(s: str) -> str:
      return ' '.join(word[::-1] for word in s.split(' '))