made translation lazy

InvenTree/label/api.py

@@ -1,7 +1,7 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
-from django.utils.translation import ugettext as _
+from django.utils.translation import ugettext_lazy as _
 from django.conf.urls import url, include
 from django.core.exceptions import ValidationError, FieldError
 from django.http import HttpResponse