Update changelog

Author: coder-hugo

CHANGELOG.md

@@ -1,6 +1,17 @@
 ChangeLog
 =====================
 
+1.4.0
+=====================
+* Breaking changes for some Pipeline jobs (see [migration guide](https://github.com/jenkinsci/gitlab-plugin/wiki/Migration-Guides) for more information)
+* Cleanup UI for GitLabPushTrigger
+* #201: customize notes for merge requsts
+* #168: MR Voting Broken after Gitlab 8.2
+* #190: Add option to mark unstable builds as success in GitLab
+* #345: Configurable "Add note with build status on merge requests"
+* Add Notifier and workflow step for accepting a MR on success
+* Add workflow step for adding comments to a MR
+
 1.3.2
 =====================
 * JENKINS-36863: Credentials drop-down doesn't show API token credential! (finally fixed it)