Update widget alert to the new syntax

(cherry picked from commit 40fc5082)

aleksis/apps/chronos/templates/chronos/widget.html

@@ -13,14 +13,12 @@
       {% if has_plan %}
         {% include "chronos/partials/lessons_col.html" with lesson_periods=lesson_periods %}
       {% else %}
-        <div class="alert warning">
-          <p>
-            <i class="material-icons left">info</i>
-            {% blocktrans %}
-              There is no timetable linked to your person.
-            {% endblocktrans %}
-          </p>
-        </div>
+        <figure class="alert warning">
+          <i class="material-icons left">info</i>
+          {% blocktrans %}
+          There is no timetable linked to your person.
+          {% endblocktrans %}
+        </figure>
       {% endif %}
     </div>
   </div>