Postorius (#241)

* Remove the secret key.

* Use the latest tag for postorius.

* Use the latest django-mailman3 that supports Python 3.

* Use minimum version on Django-mailman3.

* Fix import errors.

postorius/mailman-web/urls.py

@@ -17,8 +17,9 @@
 # Postorius.  If not, see <http://www.gnu.org/licenses/>.
 
 
-from django.conf.urls import include, url, reverse_lazy
+from django.conf.urls import include, url
 from django.contrib import admin
+from django.urls import reverse_lazy
 from django.views.generic import RedirectView
 
 urlpatterns = [