Fix whitespace issues on roadmap

See https://hifis.net/roadmap

Before	Now

_layouts/roadmap.html

@@ -54,7 +54,7 @@
                     <h2>{{ date_item | date: "%B %Y" }}</h2>
                 </div>
                 {%- else -%}
-                <div class="p-3"></div>
+                <div class="p-3 {{ hidden_class }}"></div>
                 {%- endif -%}
                 {% assign month = roadmap_month %}
                 <div class="roadmap-item {{ hidden_class }}">