input: Write a python function to sort a list of tuples by the second item.
  assert sort_tuples([('Alice', 20), ('Bob', 30), ('Andrew', 20), ('Catherine', 40)]) == [('Alice', 20), ('Andrew', 20), ('Bob', 30), ('Catherine', 40)]
  assert sort_tuples([('Tom', 5), ('Jerry', 15), ('Mickey', 10), ('Donald', 5)]) == [('Tom', 5), ('Donald', 5), ('Mickey', 10), ('Jerry', 15)]
  assert sort_tuples([('X', 100), ('Y', 1), ('Z', 50), ('W', 75)]) == [('Y', 1), ('Z', 50), ('W', 75), ('X', 100)]
output: def sort_tuples(tuples_list):
      return sorted(tuples_list, key=lambda x: x[1])