Update CHANGELOG

CHANGELOG

@@ -39,6 +39,7 @@ v 8.8.0 (unreleased)
   - Expire repository exists? and has_visible_content? caches after a push if necessary
   - Fix unintentional filtering bug in issues sorted by milestone due (Takuya Noguchi)
   - Fix adding a todo for private group members (Ahmad Sherif)
+  - Bump ace-rails-ap gem version from 2.0.1 to 4.0.2 which upgrades Ace Editor from 1.1.2 to 1.2.3
 
 v 8.7.4
   - Fix always showing build notification message when switching between merge requests