test: normalize fixtures use

This commit replaces the use of `common.fixturesDir`
with `common.fixtures` & `fixtures.path` in
`test-fs-read-stream-resume.js`

PR-URL: https://github.com/nodejs/node/pull/15855


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>