Resolve "style.scss uses deprecated SCSS"

Closes #410 (closed)

aleksis/core/static/style.scss

@@ -400,7 +400,7 @@ th.orderable > a {
 }
 
 th.orderable > a::after {
-  @extend i.material-icons;
+  @extend .material-icons;
   font-family: 'Material Icons';
   font-weight: normal;
   font-style: normal;