add index class to article.html

layouts/partials/article.html

@@ -1,4 +1,4 @@
-<article class="float-on-hover">
+<article class="index float-on-hover">
     <a href=" {{ .Permalink }}">
     	{{- $image := (.Resources.GetMatch "featured").Resize "256x webp q90" }}
         <img src={{ $image.RelPermalink }} alt="{{ .Params.featured.alt }}">