Add back missing newline

Author: dmurvihill

src/index.js

@@ -9,4 +9,4 @@ exports.MockFirestore = require('./firestore');
 exports.MockStorage = require('./storage');
 exports.MockMessaging = require('./messaging');
 exports.DeltaDocumentSnapshot = MockFirestoreDeltaDocumentSnapshot.create;
-exports.DataSnapshot = require('./snapshot');
+exports.DataSnapshot = require('./snapshot');