input: Write a python function to double the elements in a list.
  assert double_list([1, 2, 3, 4, 5]) == [2, 4, 6, 8, 10]
  assert double_list([10, 20, 30, 40]) == [20, 40, 60, 80]
  assert double_list([0, -1, -2, -3]) == [0, -2, -4, -6]
output: def double_list(lst):
      return [x * 2 for x in lst]