Dead installation link in vagrant documentation

If you click on `installation in

(Step 6) https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/vagrant.md#vagrant-with-virtualbox

or

(Step 5) https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/vagrant.md#vagrant-with-docker

the link leads to nowhere. I think it should go to https://gitlab.com/gitlab-org/gitlab-development-kit/blob/master/doc/set-up-gdk.md but I'm not certain