Convert self.artifacts to TYPES.

Library/Homebrew/cask/lib/hbc/artifact.rb

@@ -27,8 +27,7 @@ module Hbc
   module Artifact
     # NOTE: order is important here, since we want to extract nested containers
     #       before we handle any other artifacts
-    def self.artifacts
-      [
+    TYPES = [
       PreflightBlock,
       NestedContainer,
       Installer,
@@ -53,13 +52,12 @@ module Hbc
       Uninstall,
       PostflightBlock,
       Zap,
-      ]
-    end
+    ].freeze
 
     def self.for_cask(cask, command: SystemCommand, force: false)
       odebug "Determining which artifacts are present in Cask #{cask}"
 
-      artifacts
+      TYPES
         .select { |klass| klass.me?(cask) }
         .map { |klass| klass.new(cask, command: command, force: force) }
     end