input: Write a python function to reverse a list.
  assert reverseList([1, 2, 3, 4, 5]) == [5, 4, 3, 2, 1]
  assert reverseList([10, 20, 30, 40, 50]) == [50, 40, 30, 20, 10]
  assert reverseList([3, 6, 9]) == [9, 6, 3]
output: def reverseList(lst):
      return lst[::-1]