GitLab

As pointed out by Matthieu, we do not need sudo to use Docker. As per
the rule of least privilege, stop asking for it.

On the one hand perl-5.10 is not available under Xenial (which is in the
process of becoming the default Travis build environment) so requesting
it would cause a build failure, on the other we do not actually USE perl
here - all the testing happens inside a Docker container. Just get rid
of this.

Travis: Do not explicitly request Linux distribution

For consistency with the other eHive repositories

* [ENSCORESW-3077] Travis: Unify configuration of Slack notifications

...but notify #ehive-commits as well.

We still need to run cpan for ensembl-hive-htcondor's dependencies