fix hard coded prefix

Author: llz

src/traits/LfmHelpers.php

@@ -110,7 +110,7 @@ public function getPathPrefix($type)
         }
 
         if ($type === 'url' && $base_directory !== 'public') {
-            $prefix = 'laravel-filemanager/' . $prefix;
+            $prefix = config('lfm.prefix', 'laravel-filemanager') . '/' . $prefix;
         }
 
         return $prefix;