fix deprecated ugettext_lazy

Author: Vlsarro

coupons/admin.py

@@ -1,7 +1,7 @@
 from django.conf.urls import url
 from django.contrib import admin
 from django.contrib import messages
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 from django.views.generic.base import TemplateView
 
 from .forms import CouponGenerationForm

coupons/forms.py

@@ -1,5 +1,5 @@
 from django import forms
-from django.utils.translation import ugettext_lazy as _
+from django.utils.translation import gettext_lazy as _
 
 from .models import Coupon, CouponUser, Campaign
 from .settings import COUPON_TYPES