cleanInfoFields 'files tree' to 'file tree'

Change cleanInfoFields 'files tree' to 'file tree' in $allowedKeys. Currently it will remove 'file tree' and result in parse errors.

Author: pandabadger

src/TorrentFile.php

@@ -307,7 +307,7 @@ public function cleanInfoFields($allowedKeys = [
         $allowedKeys = array_merge([
             'name', 'private', 'piece length', // Common key
             'files', 'pieces', 'length',  // v1
-            'files tree', 'meta version', // v2
+            'file tree', 'meta version', // v2
         ], $allowedKeys);
         foreach ($this->data['info'] as $key => $value) {
             if (!in_array($key, $allowedKeys)) {