Add default value at route prefix

Author: Rohos

src/routes.php

@@ -1,6 +1,6 @@
 <?php
 $middlewares = \Config::get('lfm.middlewares');
-$prefix = \Config::get('lfm.prefix');
+$prefix = \Config::get('lfm.prefix', 'laravel-filemanager');
 array_push($middlewares, '\Unisharp\Laravelfilemanager\middleware\MultiUser');
 //, 'as' => 'admin.'
 // make sure authenticated