fix name error for HttpResponseNotFound

frontend/views.py

@@ -23,7 +23,7 @@ from django.contrib import messages
 from django.forms import Select
 from django.forms.models import modelformset_factory
 from django.http import HttpResponseRedirect
-from django.http import HttpResponse
+from django.http import HttpResponse, HttpResponseNotFound
 from django.views.decorators.csrf import csrf_exempt
 from django.views.decorators.http import require_POST
 from django.views.generic.edit import FormView