input: Write a python function to calculate the average or maximum of a list of numbers.
  assert calc_average([1, 2, 3, 4, 5]) == 3.0
  assert calc_average([10, 20, 30, 40, 50], maximum=True) == 50
  assert calc_average([5, 10, 15], maximum=False) == 10.0
output: def calc_average(numbers, maximum=False):
      if maximum:
          return max(numbers)
      else:
          return sum(numbers) / len(numbers)