message: Update reverse-string.py
diff: class Solution(object):
  def reverseString(self, s):
  """
  - :type s: str
  - :rtype: str
  + :type s: List[str]
  + :rtype: None Do not return anything, modify s in-place instead.
  """
  i, j = 0, len(s) - 1
  while i < j:
  s[i], s[j] = s[j], s[i]
  i += 1
  j -= 1
  - return s
  -
  