Fixed string interpolation on template name

Current version doesn't compile due to template name interpolation issues:

       ArgumentError
       -------------
       You must supply a name when declaring a template resource
       
       
       Cookbook Trace:
       ---------------
         /tmp/kitchen/cookbooks/varnish/recipes/default.rb:34:in `from_file'
         /tmp/kitchen/cookbooks/carrenza-varnish/recipes/default.rb:21:in `from_file'