dns: switch var to const/let

Simple exchange var to const/let.

PR-URL: #30302
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

lib/dns.js

@@ -73,7 +73,7 @@ function onlookupall(err, addresses) {
   }
 
   const family = this.family;
-  for (var i = 0; i < addresses.length; i++) {
+  for (let i = 0; i < addresses.length; i++) {
     const addr = addresses[i];
     addresses[i] = {
       address: addr,
@@ -88,10 +88,10 @@ function onlookupall(err, addresses) {
 // Easy DNS A/AAAA look up
 // lookup(hostname, [options,] callback)
 function lookup(hostname, options, callback) {
-  var hints = 0;
-  var family = -1;
-  var all = false;
-  var verbatim = false;
+  let hints = 0;
+  let family = -1;
+  let all = false;
+  let verbatim = false;
 
   // Parse arguments
   if (hostname && typeof hostname !== 'string') {
@@ -206,7 +206,7 @@ function onresolve(err, result, ttls) {
 
 function resolver(bindingName) {
   function query(name, /* options, */ callback) {
-    var options;
+    let options;
     if (arguments.length > 2) {
       options = callback;
       callback = arguments[2];
@@ -248,7 +248,7 @@ Resolver.prototype.reverse = resolver('getHostByAddr');
 Resolver.prototype.resolve = resolve;
 
 function resolve(hostname, rrtype, callback) {
-  var resolver;
+  let resolver;
   if (typeof rrtype === 'string') {
     resolver = resolveMap[rrtype];
   } else if (typeof rrtype === 'function') {