Update unit-test.stub to use RefreshDatabase trait

[techenby]

Since Illuminate\Foundation\Testing\RefreshDatabase is used by default now, this stub should reflect it and match the test.stub.

[lucasmichot]

As this is a stub, this is kept as it on purpose

[techenby]

Then why was the test.stub updated? https://github.com/laravel/framework/blob/master/src/Illuminate/Foundation/Console/stubs/test.stub

When running php artisan make:test ModelTest --unit, on a 5.5 project I currently get the old database migration and transaction traits, instead of the new RefreshDatabase trait.

But when I run php artisan make:test ExampleTest on the same project I do get the RefreshDatabase trait.

It doesn't make sense to have it in one place but not the other, but if it was done on purpose, feel free to close the PR.