style(core): add missing type annotation

Author: vsavkin

modules/core/src/dom/element.js

@@ -2,7 +2,7 @@ import {Element} from 'facade/dom';
 
 export class NgElement {
   domElement:Element;
-  constructor(domElement) {
+  constructor(domElement:Element) {
     this.domElement = domElement;
   }
 }