Update custom.php

Author: tabacitu

src/routes/backpack/custom.php

@@ -8,7 +8,7 @@
 
 Route::group([
     'prefix'     => config('backpack.base.route_prefix', 'admin'),
-    'middleware' => [backpack_middleware()],
+    'middleware' => [config('backpack.base.middleware_key', 'admin')],
     'namespace'  => 'App\Http\Controllers\Admin',
 ], function () { // custom admin routes
 }); // this should be the absolute last line of this file