Update release notes

RELEASE_NOTES.md

@@ -1,22 +1,5 @@
 
-Bacularis 4.2.0 introduces support for a plugin interface on the API side.
-So, since now users are able to create own API-side plugins in the same way
-as they can already create Web-side plugins. For a good start we provided
-a Bacula configuration plugin interface and we prepared first API plugin for
-attaching pre/post config actions.
-
-On the Bacula deployment side, we extended support for Bacula packages from
-bacula.org. It significantly simplifies configuring OS profiles to use
-bacula.org packages. It causes that using system Bacula packages, packages
-from bacula.org or packages provided in self-hosted package repository can
-easily be configured in the OS profile.
-
-This version is also bug fix release. We fixed couple of bugs found in
-the deployment function.
-
-**Changes**
- - Extended support for deploying with Bacula packages from bacula.org
- - Unify using Web plugins
- - Improve displaying dashboard totals on medium screens
- - Move table toolbar function to Common
+In Bacularis 4.2.0 we found a non-existing module definition that causes
+Bacularis break. Bacularis 4.2.1 is a bug fix release that fixes this
+error.