Replace usage of old-style WHATWG spec links

components/script/dom/webidls/HTMLDialogElement.webidl

@@ -3,7 +3,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-// https://www.whatwg.org/html/#htmldialogelement
+// https://html.spec.whatwg.org/multipage#htmldialogelement
 interface HTMLDialogElement : HTMLElement {
   attribute boolean open;
   attribute DOMString returnValue;