Bump gitlab-shell version to match migration guide

@jgrowl

Great work refactoring the playbook!  One issue I ran into is that the gitlab-shell version isn't matching what the gitlabhq migration guide says it should be.

https://github.com/gitlabhq/gitlabhq/blob/master/doc/update/5.3-to-5.4.md

You can see that by running the check that they recommend:

```
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production
```

By the way, the check also complains that the init script isn't up-to-date, but I haven't checked on that yet.  The other issue I ran into was that I couldn't restore a backup due to the mysql user permissions, but I'll try to open a separate issue about that.