deps: update llhttp to 6.0.4

Refs: https://hackerone.com/reports/1238099
Refs: https://hackerone.com/reports/1238709
Refs: https://github.com/nodejs-private/llhttp-private/pull/6
Refs: https://github.com/nodejs-private/llhttp-private/pull/5
CVE-ID: CVE-2021-22959
CVE-ID: CVE-2021-22960

PR-URL: https://github.com/nodejs-private/node-private/pull/284


Reviewed-By: Akshay K <iit.akshay@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Robert Nagy <ronagy@icloud.com>