Fix data binding expression in the example (#188)
Fix data binding expression in the example (#188)

- "item.name" is not an observable so we can't use the async pipe on it.
- use the safe navigation operator to access the name property of the retrieved object.
maneesht/angularfire2,maneesht/angularfire2,angular/angularfire,angular/angularfire,maneesht/angularfire2,angular/angularfire,maneesht/angularfire2,angular/angularfire