Fix css decision for substition highlighting.

biscuit/apps/chronos/tables.py

@@ -10,7 +10,7 @@ from .models import LessonPeriod
 
 
 def _css_class_from_lesson_state(record: Optional[LessonPeriod] = None, table: Optional[LessonsTable] = None) -> str:
-    if record.get_substitution(table._week):
+    if record.get_substitution(record._week):
         return 'table-warning'
     else:
         return ''