fix: eloquent model import

[badasukerubin]

Thank you for this great package.
When I tested the package within another Laravel package, I got Class "Workflow\Models\Model" not found.
I was able to temporarily circumvent the issue by creating an alias in the package's ServiceProvider ie:

...
use Illuminate\Database\Eloquent\Model;
...

 if (! class_exists('Workflow\Models\Model')) {
            class_alias(
                Model::class,
                'Workflow\Models\Model'
            );
        }

, but it'd be nice not to get the error at all.

[rmcdaniel]

That is actually intentional and how it's meant to loaded. That's because some packages like MongoDB do not extend the Eloquent models.

https://github.com/laravel-workflow/laravel-workflow/blob/master/src/Providers/WorkflowServiceProvider.php#L30

Thank you for the PR anyways. I appreciate the time and effort you took to make it.