Fix typo.

biscuit/apps/chronos/forms.py

@@ -24,4 +24,4 @@ class SelectForm(forms.Form):
 class LessonSubstitutionForm(forms.ModelForm):
     class Meta:
         model = LessonSubstitution
-        fields = ['week', 'lesson_period', 'subject', 'teachers', 'room', 'canceled']
+        fields = ['week', 'lesson_period', 'subject', 'teachers', 'room', 'cancelled']

biscuit/apps/chronos/templates/chronos/tt_lesson.html

 {# -*- engine:django -*- #}
 
-{% if not lesson_period.get_substitution.canceled %}
+{% if not lesson_period.get_substitution.cancelled %}
   <div class="card chronos-lesson
     {% if lesson_period.get_substitution %}
     border border-warning