Update CHANGELOG.md for 10.5.7

CHANGELOG.md

@@ -2,6 +2,14 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
 
+## 10.5.7 (2018-04-03)
+
+### Security (2 changes)
+
+- Fix XSS on diff view stored on filenames.
+- Adds confidential notes channel for Slack/Mattermost.
+
+
 ## 10.5.6 (2018-03-16)
 
 ### Security (2 changes)

changelogs/unreleased/42028-xss-diffs.yml

----
-title: Fix XSS on diff view stored on filenames
-merge_request:
-author:
-type: security

changelogs/unreleased/jej-mattermost-notification-confidentiality.yml

----
-title: Adds confidential notes channel for Slack/Mattermost
-merge_request:
-author:
-type: security