Notification being passed instead of notifiable [v1, L8]

Referencing this PR
https://github.com/laravel-notification-channels/google-chat/pull/14

However, this was only available on V3 (only compatible with L9+). Could we possibly get a fix for V1, for L8? I see it would be the same exact changes, 1:1. 

Please let me know if there's anything I can do to help.

Thanks!