Update src/Gaufrette/Adapter/Ftp.php

Co-authored-by: Kévin <kevinar9@outlook.fr>

src/Gaufrette/Adapter/Ftp.php

@@ -449,7 +449,7 @@ private function parseRawlist(array $rawlist): array
     /**
      * Computes the path for the given key.
      */
-    private function computePath(string $key)
+    private function computePath(string $key): string
     {
         return rtrim($this->directory, '/') . '/' . $key;
     }