Variable isn't defined

[File](https://github.com/webosose/nodejs-module-webos-service/blob/master/lib/message.js#L64): `lib/message.js:64`

I'm see this code:

```javascript
this.activityManager.complete(this.activity, function(activityManagerRespnse) {
	console.log("completion callback");
});
```

But, variable `this.activity` isn't defined and doesn't exist. This is a potential bug.