input: Write a python function to sort an array in descending order.
  assert sortDesc([99, 65, 43, 87, 21])==[99, 87, 65, 43, 21]
  assert sortDesc([5, 3, 8, 6])==[8, 6, 5, 3]
  assert sortDesc([1, 2, 3, 4, 5])==[5, 4, 3, 2, 1]
output: def sortDesc(arr):
      return sorted(arr, reverse=True)