deps: upgrade npm to 6.5.0 release version

[lance]

Updates npm dependency to be the released version of 6.5.0. The current version in 11.6.0 is a pre-release version.

Fixes: #25311

~/s/node (npm-6.5.0 $>) nvm use 11.6.0
Now using node v11.6.0 (npm v6.5.0-next.0)

Running make test-npm locally as specified in the guide, there are 5 test failures. So this prompted me to check out the v6.5.0 tag of npm/cli and run the build. That produced significantly more errors.

...
total ........................................... 4797/4832
  4797 passing (10m)
  9 pending
  26 failing

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included (see note above)
• documentation is changed or added (documentation changes in upstream npm only)
• commit message follows commit guidelines

[nodejs-github-bot]

@lance build started: https://ci.nodejs.org/blue/organizations/jenkins/node-test-pull-request-lite-pipeline/detail/node-test-pull-request-lite-pipeline/2127/pipeline

[addaleax]

I think this is a duplicate of #25234 ? :)

[lance]

@addaleax you are right! Rats! Sorry about that. Closing.

[lance]

At least I learned how to update npm, so it wasn't all for naught.