input: Write a function to calculate the sum of numbers entered by the user until 'done' is entered.
  assert sum_of_numbers(["1", "2", "3", "done"]) == 6
  assert sum_of_numbers(["5", "10", "15", "done"]) == 30
  assert sum_of_numbers(["0", "-1", "-2", "done"]) == -3
output: def sum_of_numbers(inputs):
      total = 0
      for num in inputs:
          if num == 'done':
              break
          total += int(num)
      return total