RELEASE-NOTES: Fix 3.3.1 release date

Author: mariushoch

RELEASE-NOTES.md

@@ -3,7 +3,7 @@ These are the release notes for the [Diff library](README.md).
 Latest release:
 [![Latest Stable Version](https://poser.pugx.org/diff/diff/version.png)](https://packagist.org/packages/diff/diff)
 
-## Version 3.3.1 (2022-10-05)
+## Version 3.3.1 (2022-10-06)
 
 * Made our __unserialize declarations match PHP 7's, to avoid PHP warnings