Hide TOC on mobile

inst/bulma/bulma.html

@@ -140,7 +140,7 @@ $endif$ <!-- bulma.hero_links -->
       </div>
     </div>
     $if(toc)$
-    <div class="column">
+    <div class="column is-hidden-mobile">
       <aside class="menu" id="toc-aside" data-gumshoe>
         $table-of-contents$
       </aside>