update SDK_VERSION to the latest value in firebase/app (#4283)

* update SDK_VERSION in `firebase/app`

* Create twenty-scissors-exist.md

Author: Feiyang1

.changeset/twenty-scissors-exist.md

@@ -0,0 +1,5 @@
+---
+"firebase": patch
+---
+
+set firebase.SDK_VERSION to the latest value

packages/firebase/app/index.ts

@@ -19,5 +19,6 @@ import firebase from '@firebase/app';
 import { name, version } from '../package.json';
 
 firebase.registerVersion(name, version, 'app');
+firebase.SDK_VERSION = version;
 
 export default firebase;