input: Write a function to replace all spaces in a string with hyphens.
  assert replace_spaces("The quick brown fox") == "The-quick-brown-fox"
  assert replace_spaces("Hello World") == "Hello-World"
  assert replace_spaces("a b c d e f g") == "a-b-c-d-e-f-g"
output: def replace_spaces(s: str) -> str:
      return s.replace(' ', '-')