input: Write a python function to replace the word "dog" with "cat" in a given string.
  assert replace_word("I love my dog") == "I love my cat"
  assert replace_word("The dog is barking") == "The cat is barking"
  assert replace_word("No dogs allowed") == "No cats allowed"
output: def replace_word(s: str) -> str:
      return s.replace("dog", "cat").replace("dogs", "cats")