Step 8.7: Helper currentUser does not return Mongo.Cursor

According to documentation[1], Angular helpers must always return Mongo.Cursor. However step 8.7 [2] defines a currentUser helper which does not return Mongo.Cursor:

```
currentUser() {
return Meteor.user();
}
```

[1] http://www.angular-meteor.com/api/1.3.11/helpers
[2] https://www.meteor.com/tutorials/angular/adding-user-accounts

Compare Step 8.7 in the Meteor tutorial with the linked angular-meteor helper documentation, focusing on the currentUser example and its return value. Determine the intended correction, then update the tutorial material so the example and documentation agree; done means the reported inconsistency is resolved.

Written by the indexing model from the issue text.