input: Write a python function to find the first word alphabetically larger than the target.
  assert find_next_word(["apple", "banana", "cherry", "date"], "apple") == "banana"
  assert find_next_word(["apple", "banana", "cherry", "date"], "banana") == "cherry"
  assert find_next_word(["apple", "banana", "cherry", "date"], "date") == None
output: def find_next_word(words, target):
      for word in words:
          if word > target:
              return word
      return None