tools: avoid using process.cwd in tools/lint-js

The first occurrence of path.join() can easily be replaced with
path.resolve().
The second occurrence should be unnecessary as ESLint will resolve the
path internally, and the old check probably did not work as intended
anyway.

PR-URL: https://github.com/nodejs/node/pull/17121


Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>