优化一下代码

Author: jiangzhonglian

docs/Leetcode_Solutions/007._Reverse_Integer.md

@@ -102,6 +102,6 @@ class Solution:
         """
         mark = 1 if x>=0 else -1
         x_abs = abs(x)
-        result = mark * int(''.join(str(x_abs)[::-1]))
+        result = mark * int(str(x_abs)[::-1])
         return result if -2**31 <= result <= 2**31-1 else 0
 ```