input: Write a python function to double the values in a list.
  assert double_values([1, 2, 3, 4]) == [2, 4, 6, 8]
  assert double_values([5, 10, 15]) == [10, 20, 30]
  assert double_values([0, -1, -2]) == [0, -2, -4]
output: def double_values(lst):
      return [x * 2 for x in lst]