Moving an issue to another project doesn't close the old issue

I've noticed this a few times. When you move an issue to another project, the old issue doesn't close.

Example: https://gitlab.com/gitlab-org/kubernetes-gitlab-demo/issues/6 was moved to https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2171, but https://gitlab.com/gitlab-org/kubernetes-gitlab-demo/issues/6 was not automatically closed.

cc @grzesiek since you implemented the feature :)