Support for sortlist missing

[Punicaa]

The cookbook is missing the option to add sortlists to resolv.conf. It should be a pretty minimal code change to fix this. If i'm correct the only thing needing to be added is the following to resolv.conf template:

<% unless nil_or_empty?(@sortlist) -%>
sortlist <%= @sortlist.join(' ') %>
<% end -%>

I've made the following PR which adds this: https://github.com/sous-chefs/resolver/pull/78