input: Write a python function to sort a dictionary by its values in descending order.
  assert sortDictionary({'apple': 2, 'banana': 3, 'mango': 1}) == {'banana': 3, 'apple': 2, 'mango': 1}
  assert sortDictionary({'a': 5, 'b': 2, 'c': 7, 'd': 4}) == {'c': 7, 'a': 5, 'd': 4, 'b': 2}
  assert sortDictionary({'x': 10, 'y': 20, 'z': 15}) == {'y': 20, 'z': 15, 'x': 10}
output: def sortDictionary(d):
      return dict(sorted(d.items(), key=lambda item: item[1], reverse=True))