Fix bug

Author: zw963

src/markd/renderers/html_renderer.cr

@@ -15,12 +15,12 @@ module Markd
 
       if entering
         newline
-        tag("div", "header-wrapper") do
+        tag("div", {class: "header-wrapper"}) do
           tag(tag_name, attrs(node))
           case toc
           when String
             toc(node, toc)
-          when True
+          when true
             toc(node)
           end
         end