migration to bootstrap 4

comic/templates/comic/breadcrumbs.html

@@ -1,7 +1,7 @@
 {% for crumb in breadcrumbs %}
     {% if not forloop.last %}
-        <li><a href="{{ crumb.url }}">{{ crumb.name }}</a></li>
+        <li class="breadcrumb-item"><a href="{{ crumb.url }}">{{ crumb.name }}</a></li>
     {% else %}
-        <li class="active">{{ crumb.name }}</li>
+        <li class="breadcrumb-item active" aria-current="page">{{ crumb.name }}</li>
     {% endif %}
 {% endfor %}