settings: use re_path directly

instead of deprecated alias `url`

tests/demo_project/demo_project/urls.py

@@ -1,10 +1,10 @@
-from django.conf.urls import url
+from django.urls import re_path
 from django.contrib import admin
 
 urlpatterns = [
     # Examples:
-    # url(r'^$', 'demo_project.views.home', name='home'),
-    # url(r'^blog/', include('blog.urls')),
+    # re_path(r'^$', 'demo_project.views.home', name='home'),
+    # re_path(r'^blog/', include('blog.urls')),
 
-    url(r'^admin/', admin.site.urls),
+    re_path(r'^admin/', admin.site.urls),
 ]