Merge branch 'unify-http_status.js' into 'master'

Add NOT_FOUND: 404 to http_status.js from EE

See merge request gitlab-org/gitlab-ce!19659

app/assets/javascripts/lib/utils/http_status.js

@@ -8,4 +8,5 @@ export default {
   OK: 200,
   MULTIPLE_CHOICES: 300,
   BAD_REQUEST: 400,
+  NOT_FOUND: 404,
 };