Fix syntax.

biscuit/apps/chronos/urls.py

@@ -6,6 +6,6 @@ from . import views
 urlpatterns = [
     path('timetable', views.timetable, name='timetable'),
     path('lessons', views.lessons_day, name='lessons_day'),
-    path('lessons/<when>', views.lessons_day, name='lessons_day_by_date')
+    path('lessons/<when>', views.lessons_day, name='lessons_day_by_date'),
     path('substitutions/<id>/edit', views.edit_substitution, name='edit_substitution')
 ]