test: use fixtures.path for cmd string building

PR-URL: https://github.com/nodejs/node/pull/15982
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/parallel/test-error-reporting.js

@@ -23,10 +23,10 @@
 const common = require('../common');
 const assert = require('assert');
 const exec = require('child_process').exec;
-const path = require('path');
+const fixtures = require('../common/fixtures');
 
 function errExec(script, callback) {
-  const cmd = `"${process.argv[0]}" "${path.join(common.fixturesDir, script)}"`;
+  const cmd = `"${process.argv[0]}" "${fixtures.path(script)}"`;
   return exec(cmd, function(err, stdout, stderr) {
     // There was some error
     assert.ok(err);