input: Write a function to sort a list of numbers in ascending order using bubble sort.
  assert sort_ascending([5, 1, 4, 2, 8])==[1, 2, 4, 5, 8]
  assert sort_ascending([64, 34, 25, 12, 22, 11, 90])==[11, 12, 22, 25, 34, 64, 90]
  assert sort_ascending([3, 0, -2, 5, 4])==[-2, 0, 3, 4, 5]
output: def sort_ascending(lst):
      n = len(lst)
      for i in range(n):
          for j in range(0, n-i-1):
              if lst[j] > lst[j+1]:
                  lst[j], lst[j+1] = lst[j+1], lst[j]
      return lst