input: Write a python function to find the maximum number in a list.
  assert maxNum([4, 9, 10, 11, 12]) == 12
  assert maxNum([1, 2, 3, 4, 5]) == 5
  assert maxNum([-1, -2, -3, -4, -5]) == -1
output: def maxNum(lst):
      return max(lst)