Update CHANGELOG.md for 13.3.1

[ci skip]

CHANGELOG.md

@@ -2,6 +2,14 @@
 documentation](doc/development/changelog.md) for instructions on adding your own
 entry.
 
+## 13.3.1 (2020-08-25)
+
+### Fixed (2 changes)
+
+- Fix bug when promoting an Issue with attachments to an Epic. !39654
+- Avoid creating diff position when line-code is nil. !40089
+
+
 ## 13.3.0 (2020-08-22)
 
 ### Security (2 changes)

changelogs/unreleased/236190-bugfix-issue-promote-with-attachments.yml

----
-title: Fix bug when promoting an Issue with attachments to an Epic
-merge_request: 39654
-author:
-type: fixed

changelogs/unreleased/id-fix-nil-line-codes-for-diff-positions.yml

----
-title: Avoid creating diff position when line-code is nil
-merge_request: 40089
-author:
-type: fixed