input: Write a python function to find the difference between the maximum and minimum numbers in a list.
  assert diff([10, 4, 2, 5, 7]) == 8
  assert diff([1, 2, 3, 4, 5]) == 4
  assert diff([100, 54, 23, 89, 2]) == 98
output: def diff(numbers):
      return max(numbers) - min(numbers)