Looks like Taylor changed the namespaced method just 2 hours ago. I'm guessing the update pulled in the framework update here https://github.com/laravel/framework/blob/master/src/Illuminate/Routing/RouteServiceProvider.php but didn't change your RouteServiceProvider to match so you could manually change it to match this https://github.com/laravel/laravel/blob/develop/app/Providers/RouteServiceProvider.php
UPDATE: May be obvious but also change the namespace to your actual namespace if you are using something besides 'App'
App::booted(function()
{
// Once the application has booted, we will include the default routes
// file. This "namespace" helper will load the routes file within a
// route group which automatically sets the controller namespace.
$this->namespaced('Larabook\Http\Controllers', function()
{
require app_path().'/Http/routes.php';
});
});