input: Write a python function to find the minimum and maximum values in a list.
  assert min_max([3, 4, 2, 8, 15, 6])==[2, 15]
  assert min_max([1, 2, 3, 4, 5])==[1, 5]
  assert min_max([-10, 0, 10, 20, -20])==[-20, 20]
output: def min_max(lst):
      return [min(lst), max(lst)]