update changelog

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.13.1
-  - Revert issue caching
+  - Fix: Label modifications are not reflected in existing notes and in the issue list
+  - Fix: Label not shown in the Issue list, although it's set through web interface
+  - Fix: Group/project references are linked incorrectly
   - Improve documentation
   - Fix of migration: Check if session_expire_delay column exists before adding the column
-  - Reverted cache for events
+  - Fix: ActionView::Template::Error
 
 v 7.13.0 (unreleased)
   - Remove repository graph log to fix slow cache updates after push event (Stan Hu)