Link to CI runner changelog for 11.6.0-rc1
GitLab Runner wasn't tagged v11.6.0
at the time the release post was merged causing the link to break: https://gitlab.com/gitlab-org/gitlab-runner/blob/v11.6.0/CHANGELOG.md
Changes the link to point to: https://gitlab.com/gitlab-org/gitlab-runner/blob/v11.6.0-rc1/CHANGELOG.md
Once the version has been tagged, this MR can be reverted.