[database][js] Reject promise instead of resolving an error object when ref.once('value') fails

lib/modules/database/Reference.js

@@ -289,7 +289,7 @@ export default class Reference extends ReferenceBase {
       })
       .catch(error => {
         if (isFunction(cancelOrContext)) return cancelOrContext(error);
-        return error;
+        throw error;
       });
   }