test: refactor test-tls-0-dns-altname

* var -> const, let
* assert.equal() -> assert.strictEqual()

PR-URL: https://github.com/nodejs/node/pull/9948
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Italo A. Casas <me@italoacasas.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-tls-0-dns-altname.js

@@ -1,16 +1,16 @@
 'use strict';
-var common = require('../common');
-var assert = require('assert');
+const common = require('../common');
+const assert = require('assert');
 
 if (!common.hasCrypto) {
   common.skip('missing crypto');
   return;
 }
-var tls = require('tls');
+const tls = require('tls');
 
-var fs = require('fs');
+const fs = require('fs');
 
-var server = tls.createServer({
+const server = tls.createServer({
   key: fs.readFileSync(common.fixturesDir + '/keys/0-dns-key.pem'),
   cert: fs.readFileSync(common.fixturesDir + '/keys/0-dns-cert.pem')
 }, function(c) {
@@ -19,11 +19,11 @@ var server = tls.createServer({
     server.close();
   });
 }).listen(0, common.mustCall(function() {
-  var c = tls.connect(this.address().port, {
+  const c = tls.connect(this.address().port, {
     rejectUnauthorized: false
   }, common.mustCall(function() {
-    var cert = c.getPeerCertificate();
-    assert.equal(cert.subjectaltname,
+    const cert = c.getPeerCertificate();
+    assert.strictEqual(cert.subjectaltname,
                        'DNS:google.com\0.evil.com, ' +
                            'DNS:just-another.com, ' +
                            'IP Address:8.8.8.8, ' +