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]) == [40, 30, 20, 10]
  assert reverseList([7, 8, 9]) == [9, 8, 7]
output: def reverseList(lst):
      return lst[::-1]