added circle.yml file to specify node version

circle.yml

@@ -0,0 +1,4 @@
+machine:
+  node:
+    version: 8.0.0
+

server/portal_server.js

@@ -89,7 +89,7 @@ app.post('/delete/:id', (req, res) => {
   const id = req.params.id;
 
   if (!validateID(id)) {
-    res.send(404);
+    res.sendStatus(404);
     return;
   }