input: Write a python function to return the squares of a list of numbers.
  assert square_numbers([1, 2, 3, 4, 5])==[1, 4, 9, 16, 25]
  assert square_numbers([10, 20, 30])==[100, 400, 900]
  assert square_numbers([0, -1, -2])==[0, 1, 4]
output: def square_numbers(numbers):
      return [x ** 2 for x in numbers]