test: use const instead of var in test-require-json.js

PR-URL: https://github.com/nodejs/node/pull/9904
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-require-json.js

@@ -1,12 +1,12 @@
 'use strict';
-var common = require('../common');
-var path = require('path');
-var assert = require('assert');
+const common = require('../common');
+const path = require('path');
+const assert = require('assert');
 
 try {
   require(path.join(common.fixturesDir, 'invalid.json'));
 } catch (err) {
-  var re = /test[/\\]fixtures[/\\]invalid.json: Unexpected string/;
-  var i = err.message.match(re);
+  const re = /test[/\\]fixtures[/\\]invalid.json: Unexpected string/;
+  const i = err.message.match(re);
   assert.notStrictEqual(null, i, 'require() json error should include path');
 }