This has introduced a regression that has broken our MTA (Postfix), based on the camptocamp-postfix module.
Steps to reproduce on Ubuntu 18.04 LTS:
```
dpkg -i puppet6-release-bionic.deb
apt update;apt install -y puppet-agent
puppet module install camptocamp-postfix --version 1.8.0
puppet apply -e 'include ::postfix'
```
Output: Error: Could not prefetch mailalias provider 'aliases': Could not parse line "postmaster: root" (file: /etc/aliases, line: 3)
Error: Failed to apply catalog: Could not parse line "postmaster: root" (file: /etc/aliases, line: 3)