Fix update/create documentation mutation

aleksis/apps/alsijil/schema/documentation.py

+from datetime import datetime
 import graphene
 from graphene_django.types import DjangoObjectType
 from graphene_django_cud.mutations import (
@@ -139,19 +140,18 @@ class DocumentationCreateOrUpdateMutation(graphene.Mutation):
             dummy, lesson_event_id, datetime_start, datetime_end = id.split(";")
 
             obj = Documentation.objects.create(
-                datetime_start=datetime_start,
-                datetime_end=datetime_end,
+                datetime_start=datetime.fromisoformat(datetime_start),
+                datetime_end=datetime.fromisoformat(datetime_end),
                 lesson_event=LessonEvent.objects.get(id=lesson_event_id),
                 topic=input.topic,
                 homework=input.homework,
                 group_note=input.group_note,
             )  # TODO: Add course & subject
         else:
-            obj = Documentations.objects.get(id=id)
-            obj.update(
-                topic=input.topic,
-                homework=input.homework,
-                group_note=input.group_note,
-            )
+            obj = Documentation.objects.get(id=id)
+            obj.topic = input.topic
+            obj.homework = input.homework
+            obj.group_note = input.group_note
+            obj.save()
 
         return DocumentationCreateOrUpdateMutation(documentation=obj)