Not possible to use route:cache

[m-ristau]

First of all: Thanks for this repository.

I noticed that i can't use php artisan route:cache anymore, because the following part in LaravelServiceProvider @ 22 is using a closure.

    if ($this->app['config']['alexa.audio.proxy.enabled'])
    {
        Route::get($this->app['config']['alexa.audio.proxy.route'] . '/{audiofile}', function($audiofile) {
            return response(base64_decode($audiofile))
                ->header('Content-Type', 'application/x-mpegurl');
        });
    }

Maybe there is a chance to fix that.
Thanks in advance and keep up the good work.

Laravel: 5.5.4
PHP: 7.1.15