process: changed var to const in internal/process/promises

PR-URL: #8620
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Jackson Tian <shvyo1987@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Ilkka Myller <ilkka.myller@nodefield.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

lib/internal/process/promises.js

@@ -25,7 +25,7 @@ function setupPromises(scheduleMicrotasks) {
   }
 
   function rejectionHandled(promise) {
-    var hasBeenNotified = hasBeenNotifiedProperty.get(promise);
+    const hasBeenNotified = hasBeenNotifiedProperty.get(promise);
     if (hasBeenNotified !== undefined) {
       hasBeenNotifiedProperty.delete(promise);
       const uid = promiseToGuidProperty.get(promise);