(maint) travis: pin to puppetserver tag
(maint) travis: pin to puppetserver tag

Shortly after tagging puppetserver bumped clj-parent which broke
integrations tests. This is a temporary pin while we release 6.10.1

puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb,puppetlabs/puppetdb