message: Update peak-index-in-a-mountain-array.py
diff: # Space: O(1)
  class Solution(object):
  - def peakIndexInMountainArray(self, A):
  + def peakIndexInMountainArray(self, arr):
  """
  - :type A: List[int]
  + :type arr: List[int]
  :rtype: int
  """
  - left, right = 0, len(A)
  - while left < right:
  + left, right = 0, len(arr)-1
  + while left <= right:
  mid = left + (right-left)//2
  - if A[mid] > A[mid+1]:
  - right = mid
  + if arr[mid] > arr[mid+1]:
  + right = mid-1
  else:
  left = mid+1
  return left
  