message: Update expressive-words.py
diff: # Time: O(n + s), n is the sum of all word lengths, s is the length of S
  -# Space: O(1)
  +# Space: O(l + s), l is the max word length
  # Sometimes people repeat letters to represent extra feeling,
  # such as "hello" -> "heeellooo", "hi" -> "hiiii".
  