Fix deprecated variable access warning

Fix to remove the following warning:

    Warning: Variable access via 'fastcgi_param' is deprecated. Use '@fastcgi_param' instead. template[/etc/puppet/modules/nginx/templates/vhost/locations/fastcgi.erb]:17 (at /etc/puppet/modules/nginx/templates/vhost/locations/fastcgi.erb:17:in `block in result')