input: Write a function to find the most frequent word in a list of words.
  assert most_frequent(["apple", "banana", "apple", "orange", "banana", "banana"]) == "banana"
  assert most_frequent(["cat", "dog", "cat", "cat", "mouse", "dog"]) == "cat"
  assert most_frequent(["red", "blue", "green", "red", "blue", "red"]) == "red"
output: def most_frequent(words):
      from collections import Counter
      counter = Counter(words)
      most_common_word, _ = counter.most_common(1)[0]
      return most_common_word