benchmark: add trailing commas

PR-URL: https://github.com/nodejs/node/pull/46370
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: Moshe Atlow <moshe@atlow.co.il>
Reviewed-By: James M Snell <jasnell@gmail.com>

benchmark/string_decoder/string-decoder.js

@@ -6,7 +6,7 @@ const bench = common.createBenchmark(main, {
   encoding: ['ascii', 'utf8', 'base64-utf8', 'base64-ascii', 'utf16le'],
   inLen: [32, 128, 1024, 4096],
   chunkLen: [16, 64, 256, 1024],
-  n: [25e5]
+  n: [25e5],
 });
 
 const UTF8_ALPHA = 'Blåbærsyltetøy';