vm data not initialised in firebase function

[posva]

As pointed out in #63
When using the function syntax:

data: {
  user: 'posva'
},
firebase () {
  return {
    someRef: db.ref('users/' + this.user) // this.user === undefined
  }
}

user should not be undefined

[RobertAKARobin]

I'm still encountering this:

<widget :fbid="myKey"></widget>

var Widget = Vue.component('widget', {
	props: ['fbid'],
	firebase: function(){
		var widget = this;
		return {
			fbdata: {
				source: db.ref('/widgets').child(widget.fbid),
				asObject: true
			}
		}
	}
});

Error: Firebase.child failed: First argument was an invalid path: "undefined". Paths must be non-empty strings and can't contain ".", "#", "$", "[", or "]"