input: Write a python function to convert a list of strings to lowercase.
  assert to_lowercase(['HELLO', 'WORLD']) == ['hello', 'world']
  assert to_lowercase(['PyTHon', 'iS', 'AWesOmE']) == ['python', 'is', 'awesome']
  assert to_lowercase(['123', 'aBc', 'DEF']) == ['123', 'abc', 'def']
output: def to_lowercase(strings):
      return [s.lower() for s in strings]