fix: can't get file_list_transfer desc cause 500 error on /swagger.json api

rel/i18n/emqx_ft_api.hocon

@@ -3,7 +3,7 @@ emqx_ft_api {
 file_list.desc:
 """List all uploaded files."""
 
-file_list_transfer.desc
+file_list_transfer.desc:
 """List a file uploaded during specified transfer, identified by client id and file id."""
 
 }