Update 0031.下一个排列.md

fixed bug in python solution and display issues

problems/0031.下一个排列.md

@@ -153,7 +153,7 @@ class Solution:
                         break
                 self.reverse(nums, i, length-1)
                 break
-        else:
+            if n == 1:
                 # 若正常结束循环，则对原数组直接翻转
                 self.reverse(nums, 0, length-1)
 
@@ -164,7 +164,7 @@ class Solution:
             high -= 1
 ```
 >上一版本简化版
-'''python
+```python
 class Solution(object):
     def nextPermutation(self, nums: List[int]) -> None:
         n = len(nums)
@@ -185,7 +185,7 @@ class Solution(object):
             end -= 1
         
         return nums
-'''
+```
 
 ## Go