Update quickstart.gs for the tabs in Docs feature

This is part of an ongoing effort to update Docs API guides/documentation for the tabs feature.

docs/quickstart/quickstart.gs

@@ -23,7 +23,7 @@ function printDocTitle() {
   const documentId = '195j9eDD3ccgjQRttHhJPymLJUCOUjs-jmwTrekvdjFE';
   try {
     // Get the document using document id
-    const doc = Docs.Documents.get(documentId);
+    const doc = Docs.Documents.get({'includeTabsContent': true}, documentId);
     // Log the title  of document.
     console.log('The title of the doc is: %s', doc.title);
   } catch (err) {