Update 0058-length-of-last-word.py

[Zirafnik]

If I am not mistaken [::-1] creates a new (reversed) string, which would give that solution a space complexity of O(n).

Instead we should just use a backwards iterator.

• File(s) Modified: 0058-length-of-last-word.py
• Language(s) Used: python3
• Submission URL: https://leetcode.com/problems/length-of-last-word/submissions/1277515120/