Changing redirect url for login in laravel 5.6.3

I installed the adminlte theme and I want to create an admin area. So my url should look like :

/admin =  admin home page dashboard
/admin/login
/admin/register/

This is my route so far:

Route::group(['middleware' => 'auth'], function () {
    Route::get('/admin', ['as' => 'admin', 'uses' => 'Admin\DashboardController@index']);
});

When I access the /admin page I am redirected to /login instead of /admin/login

The redirection is made from here:

vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php

in the unauthenticated method

I followed up the answer from here: Laravel 5.5 change unauthenticated login redirect url ,but i ended up with this error:

Declaration of App\Exceptions\Handler::unauthenticated($request, App\Exceptions\AuthenticationException $exception) should be compatible with Illuminate\Foundation\Exceptions\Handler::unauthenticated($request, Illuminate\Auth\AuthenticationException $exception)

Any idea how do I change my redirect url ? Thank you

via Chebli Mohamed