Add missing variable in AJAX FAQ example

- include "isLoaded" in destructuring assignment

content/docs/faq-ajax.md

@@ -55,7 +55,7 @@ class MyComponent extends React.Component {
   }
 
   render() {
-    const { error, items } = this.state;
+    const { error, isLoaded, items } = this.state;
     if (error) {
       return <div>Error: {error.message}</div>;
     } else if (!isLoaded) {