Use weekday name in headings again.

biscuit/apps/alsijil/templates/alsijil/group_week.html

@@ -27,7 +27,7 @@
             {{ group.name }}
           </div>
           <div class="card-body">
-            {% regroup lesson_periods by period.weekday as periods_by_day %}
+            {% regroup lesson_periods by period.get_weekday_display as periods_by_day %}
             {% for weekday, periods in periods_by_day %}
               <h3>{{ weekday }}</h3>
               <table class="table table-striped table-bordered table-hover table-responsive-xl">