kube-cluster: use deprecate! instead of discontinued

Casks/k/kube-cluster.rb

@@ -6,11 +6,9 @@ cask "kube-cluster" do
   name "Kube-Cluster"
   homepage "https://github.com/TheNewNormal/kube-cluster-osx"
 
+  deprecate! date: "2023-12-17", because: :discontinued
+
   app "Kube-Cluster.app"
 
   zap trash: "~/kube-cluster"
-
-  caveats do
-    discontinued
-  end
 end