[Mailer] Move remaining DSN to new format

tucksaun · tucksaun · commit a2c607bcd751 · 2019-10-16T11:13:11.000+02:00
diff --git a/mailer.rst b/mailer.rst
@@ -749,7 +749,7 @@ environment:
     # config/packages/dev/mailer.yaml
     framework:
         mailer:
-            dsn: 'smtp://null'
+            dsn: 'null://null'
 
 .. note::
 
