Fix missing HTML tag (#583)

(cherry picked from commit 27cac869d3)

ihatemoney/templates/404.html

@@ -10,4 +10,5 @@
         <div class="col-xs-12 col-sm-5 col-md-4 offset-md-2">
           <a href='{{ url_for("main.home") }}'>{{ _("The best thing to do is probably to get back to the main page.")}}</a>
         </div>
+    </main>
 {% endblock %}