Fix artisan queue:failed-table

Not going to include a failing test as it'd just be a waste of time. 
Running `php artisan queue:failed-table` spits out "... failed to open stream: No such file or directory".

I guess this is left over from before /database was moved out of /app.
Add type in GeneratorCommand
Merge pull request #5738 from alextyrey/patch-1

Fix artisan queue:failed-table
Merge pull request #5739 from lucasmichot/5.0-generatorcommand-type

[5.0] GeneratorCommand : Missing type declaration
Merge branch 'master' of https://github.com/laravel/framework