Use module Compat style.

Library/Homebrew/compat/tap.rb

@@ -1,4 +1,5 @@
-module CaskTapMigration
+class Tap
+  module Compat
     def initialize(user, repo)
       super
 
@@ -31,8 +32,7 @@ module CaskTapMigration
       puts "Changing remote from #{old_remote} to #{new_remote}..." if $stdout.tty?
       new_path.git_origin = new_remote
     end
-end
+  end
 
-class Tap
-  prepend CaskTapMigration
+  prepend Compat
 end