Resolve "[Lesson substitution] View with all lesson substitutions in the future"

Closes #11 (closed)

biscuit/apps/chronos/urls.py

@@ -10,5 +10,5 @@ urlpatterns = [
     path('lessons/<when>', views.lessons_day, name='lessons_day_by_date'),
     path('lessons/<int:id_>/<int:week>/substition', views.edit_substitution, name='edit_substitution'),
     path('lessons/<int:id_>/<int:week>/substition/delete', views.delete_substitution, name='delete_substitution'),
-    path('substitutions', views.substitutions, name='substitutions')
+    path('substitutions/', views.substitutions, name='substitutions')
 ]