Update readme stable tag to last version

Author: cbravobernal

readme.txt

@@ -4,7 +4,7 @@ Tags: fields, custom fields, meta, scf
 Requires at least: 6.0
 Tested up to: 6.8
 Requires PHP: 7.4
-Stable tag: 6.5.5
+Stable tag: 6.5.7
 License: GPLv2 or later
 License URI: https://www.gnu.org/licenses/gpl-2.0.html