Use newer letsencrypt module, but pin to a specific commit
Use newer letsencrypt module, but pin to a specific commit

https://github.com/voxpupuli/puppet-letsencrypt/commit/2b42ade606bfd7e7f5459e953b29f584579ca2a4
causes puppet-dlrn to fail spec tests, due to [1]. The module changed
to a different namespace, so let's update it and pin it in .fixtures.yml

[1] - https://review.rdoproject.org/jenkins/job/puppet-spec/282/console

Change-Id: Ib0e8d61f498ca0e751c55920614a1936fdf93a0c

rdo-infra/puppet-dlrn,javierpena/puppet-delorean,rdo-infra/puppet-dlrn,javierpena/puppet-delorean,rdo-infra/puppet-dlrn,javierpena/puppet-delorean