Adding missing imports in the code

Author: devkiloton

snippets/database-next/read-and-write/rtdb_social_write_fan_out.js

@@ -5,6 +5,8 @@
 // 'npm run snippets'.
 
 // [START rtdb_social_write_fan_out_modular]
+import { getDatabase, ref, update, push, child } from "firebase/database";
+
 function writeNewPost(uid, username, picture, title, body) {
   const db = getDatabase();