input: Write a python function to double the elements of a list using a lambda function.
  assert double_elements([1, 2, 3, 4, 5]) == [2, 4, 6, 8, 10]
  assert double_elements([10, 20, 30]) == [20, 40, 60]
  assert double_elements([0, -1, -2]) == [0, -2, -4]
output: def double_elements(lst):
      return list(map(lambda x: x * 2, lst))