input: Write a function to multiply each number in a list by 2.
  assert times_two([1, 2, 3, 4, 5]) == [2, 4, 6, 8, 10]
  assert times_two([10, 20, 30]) == [20, 40, 60]
  assert times_two([0, -1, -2]) == [0, -2, -4]
output: def times_two(numbers):
      return [number * 2 for number in numbers]