adds required import.

site_checker_app/views.py

@@ -8,7 +8,7 @@
 from django.conf import settings as project_settings
 from django.contrib.auth import logout
 from django.core.urlresolvers import reverse
-from django.http import HttpResponse, HttpResponseRedirect
+from django.http import HttpResponse, HttpResponseNotFound, HttpResponseRedirect
 from django.shortcuts import get_object_or_404, render
 
 log = logging.getLogger(__name__)