fix wrong parameter in html-custon-elements.js

src/html-custom-element.js

@@ -66,7 +66,7 @@ export class HTMLCustomElement extends HTMLElement {
       mutations.forEach((mut) => {
         if (mut.attributeName in elem.Attr) {
           for (let fun of elem.Attr[mut.attributeName]) {
-            fun(mut.oldValue, mut.target[mut.attributeName]);
+            fun(mut.target, mut.target[mut.attributeName]);
           }
         }
       });