tools,doc: fix linting errors
We recently added linting for files in tools/doc
but PR #4741 was submitted before that tooling was added. It landed without a rebase and test run, so it's breaking CI. This fixes the minor lint issues. Hopefully this can land quickly.
/cc @fansworld-claudio @silverwind
Refs: https://github.com/nodejs/node/pull/4741#issuecomment-181973382