input: Write a python function to increment each element in a list by one.
  assert add_one([1, 2, 3]) == [2, 3, 4]
  assert add_one([0, 0, 0]) == [1, 1, 1]
  assert add_one([-1, -2, -3]) == [0, -1, -2]
output: def add_one(lst):
      return [x + 1 for x in lst]