Updated typings of admin.database.Query.once() (#300)

Author: hiranya911

CHANGELOG.md

@@ -1,5 +1,7 @@
 # Unreleased
 
+- [changed] Updated the typings of the `admin.database.Query.once()`
+  method to return a more specific type.
 - [changed] Admin SDK can now read the Firebase/GCP project ID from both
   `GCLOUD_PROJECT` and `GOOGLE_CLOUD_PROJECT` environment variables.
 

src/index.d.ts

@@ -307,7 +307,7 @@ declare namespace admin.database {
       successCallback?: (a: admin.database.DataSnapshot, b?: string) => any,
       failureCallbackOrContext?: Object|null,
       context?: Object|null
-    ): Promise<any>;
+    ): Promise<admin.database.DataSnapshot>;
     orderByChild(path: string): admin.database.Query;
     orderByKey(): admin.database.Query;
     orderByPriority(): admin.database.Query;