fix(firebase_core): Update google_services_gradle_plugin_version in pubspec (#16944)

Co-authored-by: Russell Wheatley <[email protected]>

Author: frederikstonge

packages/firebase_core/firebase_core/pubspec.yaml

@@ -44,6 +44,6 @@ flutter:
         pluginClass: FirebaseCorePluginCApi
 
 firebase:
-  google_services_gradle_plugin_version: '4.3.10'
+  google_services_gradle_plugin_version: '4.3.15'
   crashlytics_gradle_plugin_version: '2.8.1'
   performance_gradle_plugin_version: '1.4.1'