input: Write a python function to sort an array in decreasing order.
  assert sortDecreasing([4, 7, 1, 3, 5, 2])==[7, 5, 4, 3, 2, 1]
  assert sortDecreasing([10, 20, 5, 3, 8])==[20, 10, 8, 5, 3]
  assert sortDecreasing([1, 2, 3, 4, 5])==[5, 4, 3, 2, 1]
output: def sortDecreasing(arr):
      return sorted(arr, reverse=True)