software/dufs: include a trailing slash in published url

This makes urljoin works as expected and generally makes sense because
this is a collection.

software/dufs/buildout.hash.cfg

@@ -15,4 +15,4 @@
 
 [instance.cfg.in]
 filename = instance.cfg.in
-md5sum = b7da4404a3a773a8aafb88ab9785ea72
+md5sum = caddccfcec646ee4a8aad2d244c1c5d5

software/dufs/instance.cfg.in

@@ -211,7 +211,7 @@ init =
   frontend_url = urlparse(self.options['frontend-url'])
   admin_user = self.options['admin-user']
   admin_password = self.options['admin-password']
-  self.options['public-url'] = frontend_url._replace(path='/pub').geturl()
+  self.options['public-url'] = frontend_url._replace(path='/pub/').geturl()
   assert not frontend_url.username
   self.options['upload-url'] = frontend_url._replace(
     netloc=f'{admin_user}:{admin_password}@{frontend_url.netloc}').geturl()