Update longest-substring-without-repeating-characters.go

[duruyao]

• Passed in Leetecode: 919320574.
• Runtime: 9 ms, faster than 62.31% of Go online submissions.
• Memory Usage: 3 MB, less than 51.86% of Go online submissions.

[priya-thv]

the solution in CPP using hashmap and sliding window technique time [complexity:o(n^2)] (https://github.com/priya-thv/dsa-practice/blob/main/sliding%20window/length%20of%20longest%20substring.cpp)