input: Write a python function to sort a list of tuples based on the second element of each tuple.
  assert sort_tuples([(1, 2), (4, 1), (9, 10), (13, -3)]) == [(13, -3), (4, 1), (1, 2), (9, 10)]
  assert sort_tuples([(5, 6), (1, -2), (8, 0), (2, 9)]) == [(1, -2), (8, 0), (5, 6), (2, 9)]
  assert sort_tuples([(3, 4), (2, 3), (1, 2), (0, 1)]) == [(0, 1), (1, 2), (2, 3), (3, 4)]
output: def sort_tuples(lst):
      return sorted(lst, key=lambda x: x[1])