input: Write a python function to sort three strings in alphabetical order.
  assert sort_strings('apples', 'oranges', 'peaches') == ['apples', 'oranges', 'peaches']
  assert sort_strings('banana', 'apple', 'cherry') == ['apple', 'banana', 'cherry']
  assert sort_strings('dog', 'cat', 'elephant') == ['cat', 'dog', 'elephant']
output: def sort_strings(s1, s2, s3):
      return sorted([s1, s2, s3])