Update the Changelog.

CHANGELOG

@@ -21,6 +21,12 @@ v 7.9.0 (unreleased)
   - Slack username and channel options
   - Add grouped milestones from all projects to dashboard.
   - Web hook sends pusher email as well as commiter 
+v 7.8.2
+  - Fix service migration issue when upgrading from versions prior to 7.3
+  - Fix setting of the default use project limit via admin UI
+  - Fix showing of already imported projects for GitLab and Gitorious importers
+  - Fix response of push to repository to return "Not found" if user doesn't have access
+  - Fix check if user is allowed to view the file attachment
 v 7.8.1
   - Fix run of custom post receive hooks