travis: Removing Puppet 3.6
travis: Removing Puppet 3.6

We really don't need that anymore.

Icinga/puppet-icinga2,lazyfrosch/puppet-icinga2,lazyfrosch/puppet-icinga2,Icinga/puppet-icinga2-rewrite,lazyfrosch/puppet-icinga2,Icinga/puppet-icinga2-rewrite,Icinga/puppet-icinga2-rewrite,Icinga/puppet-icinga2