Stop Puppet 3 from squawking about variable access

    ...
    Fri Nov 15 19:42:12 +0000 2013 Puppet (warning): Variable access via 'hierarchy' is deprecated. Use '@hierarchy' instead. template[/etc/puppet/modules/hiera/templates/hiera.yaml.erb]:5
       (at /etc/puppet/modules/hiera/templates/hiera.yaml.erb:5:in `result')
    Fri Nov 15 19:42:12 +0000 2013 Puppet (warning): Variable access via 'datadir' is deprecated. Use '@datadir' instead. template[/etc/puppet/modules/hiera/templates/hiera.yaml.erb]:8
       (at /etc/puppet/modules/hiera/templates/hiera.yaml.erb:8:in `result')
    ...