Update urls.py to avoid namespace error (django-webpack#156)

Updating the simple/app/urls.py to avoid `django.core.exceptions.ImproperlyConfigured` error.

Author: pmarais

examples/simple/app/urls.py

@@ -16,10 +16,10 @@
 from django.conf.urls import include, url
 from django.contrib import admin
 from django.views.generic import TemplateView
-
-
+## For Django 2+ support
+from django.urls import path
 
 urlpatterns = [
  url(r'^$', TemplateView.as_view(template_name='home.html'), name='home'),
- url(r'^admin/', include(admin.site.urls)),
+ path('admin/', admin.site.urls), ## Django 2+ admin namespace
 ]