benchmark: fix invalid requirementsURL

Location of `writing-and-running-benchmarks.md` is `doc/contributing`
(not benchmark).

benchmark/_http-benchmarkers.js

@@ -5,7 +5,7 @@ const path = require('path');
 const fs = require('fs');
 
 const requirementsURL =
-  'https://github.com/nodejs/node/blob/HEAD/benchmark/writing-and-running-benchmarks.md#http-benchmark-requirements';
+  'https://github.com/nodejs/node/blob/HEAD/doc/contributing/writing-and-running-benchmarks.md#http-benchmark-requirements';
 
 // The port used by servers and wrk
 exports.PORT = Number(process.env.PORT) || 12346;