input: Write a python function to sort words in a list ignoring case.
  assert sort_words(['banana', 'Apple', 'cherry', 'apple']) == ['Apple', 'apple', 'banana', 'cherry']
  assert sort_words(['Dog', 'elephant', 'cat', 'Bee']) == ['Bee', 'cat', 'Dog', 'elephant']
  assert sort_words(['Zebra', 'giraffe', 'Antelope', 'buffalo']) == ['Antelope', 'buffalo', 'giraffe', 'Zebra']
output: def sort_words(words):
      return sorted(words, key=str.lower)