Update dependencies.

Change-Id: Ibca1be39b37f76ad9dfe743087959559d3f65d2a
diff --git a/src/main/java/eu/mulk/mulkcms2/benki/newsletter/NewsletterResource.java b/src/main/java/eu/mulk/mulkcms2/benki/newsletter/NewsletterResource.java
index 3786c9c..948ef4b 100644
--- a/src/main/java/eu/mulk/mulkcms2/benki/newsletter/NewsletterResource.java
+++ b/src/main/java/eu/mulk/mulkcms2/benki/newsletter/NewsletterResource.java
@@ -55,7 +55,7 @@
     var mailText = Templates.registrationMail(subscription.registrationKey);
     var sendJob = mailText.subject("MulkCMS newsletter registration").to(email).send();
     var page = Templates.completeRegistration().render();
-    return sendJob.thenApply((x) -> page);
+    return sendJob.onItem().transform(x -> page).subscribeAsCompletionStage();
   }
 
   @GET