input: Write a python function to sort an array in descending order.
  assert sort_array([4, 2, 9, 1, 5, 6])==[9, 6, 5, 4, 2, 1]
  assert sort_array([3, 0, -1, 8, 7, 5])==[8, 7, 5, 3, 0, -1]
  assert sort_array([10, 20, 30, 40, 50])==[50, 40, 30, 20, 10]
output: def sort_array(arr):
      return sorted(arr, reverse=True)