Fix Disconnect not being referenced in reference.js

Author: BlooJeans

lib/modules/database/reference.js

@@ -5,6 +5,7 @@ import { NativeModules } from 'react-native';
 import promisify from './../../utils/promisify';
 import { ReferenceBase } from './../base';
 import Snapshot from './snapshot.js';
+import Disconnect from './disconnect.js';
 import Query from './query.js';
 
 const FirestackDatabase = NativeModules.FirestackDatabase;