input: Write a python function to reverse each word in a sentence.
  assert reverse_sentence("Hello world!") == "olleH !dlrow"
  assert reverse_sentence("Python is fun") == "nohtyP si nuf"
  assert reverse_sentence("Keep calm and code on") == "peeK mlac dna edoc no"
output: def reverse_sentence(sentence):
      return ' '.join(word[::-1] for word in sentence.split())