Unexpected Token error in ExpressJS hello work example

Was attempting to use Webtask.io as a middleware solution in my current application, but my problem is that I can't get the express.js hello world example to work. All I want is this express server to reply "Hello Grails" when hit with a GET request. My code:
Webtask:

var express    = require('express');
var Webtask    = require('webtask-tools');
var bodyParser = require('body-parser');
var app = express();

app.use(bodyParser.json());

app.get('/', function (req, res) {
    res.send({greeting: 'Hello Grails!'})
});

module.exports = Webtask.fromExpress(app);

The error that both postman and my Grails app receive is:

{
 "code": 400,
 "message": "Compilation failed: Unexpected token <",
 "error": "Unexpected token <",
 "stack": "SyntaxError: Unexpected token <\n       
 at Object.exports.runInThisContext (vm.js:53:16)\n ... "
}

The built-in runner for webtask returns "Hello Grails", but plain get requests from Postman and my application don't. What am I doing wrong?

via K. Rhoda