Update error template to just show message and not repeat the code (#2)

app/templates/error.html

@@ -2,5 +2,5 @@
 {% block title %}{{ code }} - {{ status }}{% endblock %}
 {% block content %}
 <h1>{{ code }} - {{ status }}</h1>
-<h2 class="my-4">{{ message }}</h2>
+<h2 class="my-4">{{ message.description }}</h2>
 {% endblock %}