Don't close milestone that has open issues

[johnbillion]

If you push a tag and the corresponding milestone still has open issues, Probot semver automatically opens an issue to warn you about this, but you can still go on and publish the release.

If you publish a release and the corresponding milestone still has open issues, Probot semver shouldn't close the milestone. It could post a comment on the There are open issues stating that the release was published but there are still open issues.

And by "issues" I mean issues and PRs.