Change HTMLElement type check

Fix HTMLElement class extending problem for iOS 8 and 9

src/runtime/internal/Component.ts

@@ -132,7 +132,7 @@ export function init(component, options, instance, create_fragment, not_equal, p
 }
 
 export let SvelteElement;
-if (typeof HTMLElement !== 'undefined') {
+if (typeof HTMLElement === 'function') {
 	SvelteElement = class extends HTMLElement {
 		$$: T$$;
 		constructor() {