test: replaces common.fixturesDir usage

In test/parallel/test-repl-require.js replaces usage of
common.fixturesDir with common/fixtures.

Part of Node.js Interactive 2017 Code & Learn

PR-URL: https://github.com/nodejs/node/pull/15818


Reviewed-By: Ryan Graham <r.m.graham@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>