input: Write a function to find the minimum and maximum numbers in a list.
  assert find_min_max([1, 10, 3, 8, 6])==[1, 10]
  assert find_min_max([-1, -10, 3, 8, 6])==[-10, 8]
  assert find_min_max([5, 5, 5, 5, 5])==[5, 5]
output: def find_min_max(lst):
      return [min(lst), max(lst)]