input: Write a python function to sort a list of strings in ascending order.
  assert sort_strings(['cat', 'dog', 'apple', 'banana']) == ['apple', 'banana', 'cat', 'dog']
  assert sort_strings(['zebra', 'monkey', 'apple', 'lemon']) == ['apple', 'lemon', 'monkey', 'zebra']
  assert sort_strings(['python', 'java', 'c++', 'ruby']) == ['c++', 'java', 'python', 'ruby']
output: def sort_strings(strings):
      return sorted(strings)