Use Markdown.content_to_html

Instead of `snd Markdown.to_html`

src/task.ml

@@ -57,7 +57,7 @@ let generate_about_us target =
       (read_child_files dir (with_extension "md"))
       (fun member ->
          Metaformat.read_file_with_metadata (module Model.Person) member
-         >>> snd Markup.to_html)
+         >>> Markup.content_to_html ())
       (fun x () -> x) in
   let* current_members = read_members "metadata/current_members" in
   let* former_members = read_members "metadata/former_members" in