fix up /etc/aliases with puppet

our new-machine checklist includes

* fix `/etc/aliases`:

        ( ! grep '^root:' /etc/aliases && echo 'root: torproject-admin@torproject.org' >> /etc/aliases ) &&
        sed -i -e 's/^root:.*/root: torproject-admin@torproject.org/' /etc/aliases && newaliases

This should probably just move into puppet.