test: change fixturesDir to fixtures.path

PR-URL: nodejs#15863
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

test/sequential/test-init.js

@@ -49,7 +49,7 @@ function test(file, expected) {
 
 {
   // test-init-index is in fixtures dir as requested by ry, so go there
-  process.chdir(common.fixturesDir);
+  process.chdir(fixtures.path());
   test('test-init-index', 'Loaded successfully!');
 }