test: change var to const for require and strict equality checks

PR-URL: https://github.com/nodejs/node/pull/9892
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-require-extensions-same-filename-as-dir.js

@@ -1,9 +1,9 @@
 'use strict';
-var common = require('../common');
+const common = require('../common');
-var assert = require('assert');
+const assert = require('assert');
 
-var content = require(common.fixturesDir +
+const content = require(common.fixturesDir +
   '/json-with-directory-name-module/module-stub/one/two/three.js');
 
-assert.notEqual(content.rocko, 'artischocko');
+assert.notStrictEqual(content.rocko, 'artischocko');
-assert.equal(content, 'hello from module-stub!');
+assert.strictEqual(content, 'hello from module-stub!');