Update release notes

Author: fredericDelaporte

releasenotes.txt

@@ -3,7 +3,7 @@
 
 Release notes - NHibernate - Version 5.3.0
 
-216 issues were resolved in this release.
+217 issues were resolved in this release.
 
     ##### Possible Breaking Changes #####
         * A distributed cache may hold conflicting timestamps after upgrade for as much as twelve hours.
@@ -231,6 +231,7 @@ Release notes - NHibernate - Version 5.3.0
 
 ** Task
 
+   * #2430 Document cache.serializer setting of CoreDistributedCache #2430
    * #2397 Update GitReleaseManager
    * #2391 Use latest Firebird for AppVeyor and Travis
    * #2388 Release 5.3