test: use common.fixtures module for file path

PR-URL: #16017
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

test/parallel/test-fs-read-zero-length.js

@@ -1,9 +1,9 @@
 'use strict';
 const common = require('../common');
+const fixtures = require('../common/fixtures');
 const assert = require('assert');
-const path = require('path');
 const fs = require('fs');
-const filepath = path.join(common.fixturesDir, 'x.txt');
+const filepath = fixtures.path('x.txt');
 const fd = fs.openSync(filepath, 'r');
 const bufferAsync = Buffer.alloc(0);
 const bufferSync = Buffer.alloc(0);