Update app.js

[jogind3r]

I am proposing one addition and two changes.
The project was not working and it requires these changes to work properly.
Please review and update.

1. The app middleware was not calling next(); hence halting the app.
2. OPTIONS should be cap
3. and mongo connect should have {useMongoClient: true,}

NOTE: further more i am getting this warning. DeprecationWarning: Mongoose: mpromise (mongoose's default promise library) is deprecated, Ideas!!

[lonerz]

For the mongoose promise, I just did mongoose.Promise = global.Promise;