input: Write a function to sort a list in ascending order.
  assert sort_ascending([5, 2, 9, 1, 5, 6])==[1, 2, 5, 5, 6, 9]
  assert sort_ascending([10, 3, 8, 15, 6])==[3, 6, 8, 10, 15]
  assert sort_ascending([4, 4, 4, 4, 4])==[4, 4, 4, 4, 4]
output: def sort_ascending(lst):
      return sorted(lst)