Fix format

_layouts/dated.html

@@ -34,7 +34,7 @@
         {% endfor %}
       </header>
       <section>
-      {% if page.title %}<h1>{{page.title}}, {{page.date | date: %F}}</h1>{% endif %}
+      {% if page.title %}<h1>{{page.title}}, {{page.date | date: "%F"}}</h1>{% endif %}
       {{ content }}
 
       </section>