GOOGLE_APPLICATION_CREDENTIALS should be sufficient

After I have set the GOOGLE_APPLICATION_CREDENTIAL I still had to set the FIREBASE_CONFIG for the project ID to be set. The service account file contains the project ID so if all I have set is the GOOGLE_APPLICATION_CREDENTIALS environment variable then that should be sufficient for my project ID to be set and the FirebaseApp to be initialized. Currently setting only the GOOGLE_APPLICATION_CREDENTIALS env var, will result in a "no project id" error. Similar to #254