Switch from resources.ToCSS to css.Sass to fix deprecation warning

Author: jhenstridge

layouts/partials/head.html

@@ -13,7 +13,7 @@
   {{- template "_internal/schema.html" . -}}
   {{- template "_internal/twitter_cards.html" . -}}
 
-  {{ $css := resources.Get "css/main.scss" | resources.ToCSS (dict "outputStyle" "compressed") | fingerprint -}}
+  {{ $css := resources.Get "css/main.scss" | css.Sass (dict "outputStyle" "compressed") | fingerprint -}}
   <link rel="stylesheet" href="{{ $css.RelPermalink }}">
   <link rel="canonical" href="{{ .Permalink }}">
   <!-- Font Awesome for the icons in the footer -->