Use ugettext everywhere. Advances BiscuIT-ng#38.

biscuit/apps/exlibris/apps.py

 from django.apps import AppConfig
-from django.utils.translation import gettext_lazy as _
+from django.utils.translation import ugettext_lazy as _
 
 
 class ExlibrisConfig(AppConfig):

biscuit/apps/exlibris/menus.py

-from django.utils.translation import gettext as _
+from django.utils.translation import ugettext as _
 
 MENUS = {
     'NAV_MENU_CORE': [