metafiles: use Set.new instead of Array#to_set

Library/Homebrew/metafiles.rb

@@ -2,14 +2,14 @@ require "set"
 
 class Metafiles
   # https://github.com/github/markup#markups
-  EXTENSIONS = %w[
+  EXTENSIONS = Set.new %w[
     .adoc .asc .asciidoc .creole .html .markdown .md .mdown .mediawiki .mkdn
     .org .pod .rdoc .rst .rtf .textile .txt .wiki
-  ].to_set.freeze
-  BASENAMES = %w[
+  ].freeze
+  BASENAMES = Set.new %w[
     about authors changelog changes copying copyright history license licence
     news notes notice readme todo
-  ].to_set.freeze
+  ].freeze
 
   def self.list?(file)
     return false if %w[.DS_Store INSTALL_RECEIPT.json].include?(file)