input: Write a python function to scramble the letters of a word.
  assert len(scramble_word('hello')) == 5
  assert set(scramble_word('world')) == set('world')
  assert scramble_word('python') != 'python'
output: import random
  
  def scramble_word(word):
      word_list = list(word)
      random.shuffle(word_list)
      return ''.join(word_list)