[5.8] Improve route:list command

[seriquynh]

Instead of always passing multiple "--columns" option if you need two or more columns:

$ php artisan route:list --columns=method --columns=uri --columns=name

You can optionally use the way below:

$ php artisan route:list --columns=method,uri,name
$ php artisan route:list --columns=method --columns=uri,name

This PR doesn't break the existing behaviour of the route:list command. It just supports a bit more convenient way.