timers: correct explanation in comment

PR-URL: #35437
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/internal/timers.js

@@ -260,7 +260,7 @@ function ImmediateList() {
 }
 
 // Appends an item to the end of the linked list, adjusting the current tail's
-// previous and next pointers where applicable
+// next pointer and the item's previous pointer where applicable
 ImmediateList.prototype.append = function(item) {
   if (this.tail !== null) {
     this.tail._idleNext = item;