fixed includeHTML script

ts/includeHTML.ts

@@ -3,7 +3,7 @@ let z:HTMLCollectionOf<HTMLElement> = <HTMLCollectionOf<HTMLElement>> document.g
 for (let i:number = 0; i < z.length; i++) {
     let element:HTMLElement = z[i];
     let externalFileURL:string = <string> element.getAttribute("includeHTML");
-    if (externalFileURL != "") {
+    if (externalFileURL) {
         let xhr:XMLHttpRequest = new XMLHttpRequest();
         xhr.onreadystatechange = function() {
             if (this.readyState == 4) {