add style pedantic badge

Author: sitatec

README.md

@@ -1,6 +1,6 @@
 # firebase_database_mocks
 
-[![Pub Version](https://img.shields.io/pub/v/firebase_database_mocks)](https://pub.dev/packages/firebase_database_mocks)
+[![Pub Version](https://img.shields.io/pub/v/firebase_database_mocks)](https://pub.dev/packages/firebase_database_mocks) [![style: effective dart](https://img.shields.io/badge/style-pedantic-blue)](https://github.com/google/pedantic)
 
 Mocks library to write unit tests for FirebaseDatabase (real-time database). Get Instance
 `MockFirebaseDatabase.instance`, then pass it around your project as if it were a