input: Write a python function to find the maximum number in a list.
  assert max_number([1, 2, 3, 4, 5, 6, 7, 8, 9, 10])==10
  assert max_number([10, 20, 45, 67, 84, 93])==93
  assert max_number([5, 7, 9, 8, 6, 4, 3])==9
output: def max_number(lst):
      max_num = lst[0]
      for num in lst:
          if num > max_num:
              max_num = num
      return max_num