Update 031-Next Permutation and 048. Rotate Image

[ashtishad]

1. Changes(031 - Next Permutation)

• Divided responsibility with using functions.
• Slice is already a reference type in go, means it passes actual slice(not a copy) to functions, that's why using pointers in swap and reverse functions looks redundant in my opinion.

Discussion: https://leetcode.com/problems/next-permutation/discuss/1554932/Go-Submission-with-Explanation

2. Changes(48. Rotate Image)

• easily understandable logic.
• rotate clock-wise = 1. transpose matrix => 2. reverse(matrix[i])
• detailed explanation in comment.
• passes all testcases.

Time Complexity : O(N) Space Complexity : O(1)