Problems deploying L5.4 on Forge

I tried to push an upgraded app but got this deploy error:

php artisan optimize PHP Fatal error: Uncaught Symfony\Component\Debug\Exception\FatalThrowableError: Call to undefined method Illuminate\Events\Dispatcher::dispatch() in /home/forge/domain.com/vendor/laravel/framework/src/Illuminate/Console/Application.php:56

I found a part solution here:

https://laravel.io/forum/01-25-2017-error-on-pushing-laravel-54-upgrade-to-forge

But when I tried it I got a new error:

error: The following untracked working tree files would be overwritten by merge: bootstrap/cache/services.php Please move or remove them before you can merge.

I'm getting nowhere with this. Any pointers?

Thanks, Gary