test: fix regression in test-require-resolver.js

PR-URL: https://github.com/nodejs/node/pull/16192
Refs: https://github.com/nodejs/node/pull/15984
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>

test/parallel/test-require-resolve.js

@@ -26,7 +26,7 @@ const assert = require('assert');
 
 assert.strictEqual(
   fixtures.path('a.js').toLowerCase(),
-  require.resolve(fixtures.path('a').toLowerCase()));
+  require.resolve(fixtures.path('a')).toLowerCase());
 assert.strictEqual(
   fixtures.path('a.js').toLowerCase(),
   require.resolve(fixtures.path('a')).toLowerCase());