plistedit-pro: update livecheck

Casks/p/plistedit-pro.rb

@@ -7,9 +7,13 @@ cask "plistedit-pro" do
   desc "Property list and JSON editor"
   homepage "https://www.fatcatsoftware.com/plisteditpro/"
 
+  # The Sparkle feed can contain items on the "beta" channel, so we restrict
+  # matching to the default channel.
   livecheck do
     url "https://www.fatcatsoftware.com/plisteditpro/downloads/appcast.xml"
-    strategy :sparkle, &:short_version
+    strategy :sparkle do |items|
+      items.find { |item| item.channel.nil? }&.short_version
+    end
   end
 
   auto_updates true