input: Write a function to implement bubble sort algorithm.
  assert bubbleSort([8, 2, 11, 9, 20, 7]) == [2, 7, 8, 9, 11, 20]
  assert bubbleSort([5, 3, 8, 4, 2]) == [2, 3, 4, 5, 8]
  assert bubbleSort([1, 2, 3, 4, 5]) == [1, 2, 3, 4, 5]
output: def bubbleSort(arr):
      n = len(arr)
      for i in range(n):
          for j in range(0, n-i-1):
              if arr[j] > arr[j+1]:
                  arr[j], arr[j+1] = arr[j+1], arr[j]
      return arr