Added attr_reader disk_cleanup_size

Library/Homebrew/cleanup.rb

@@ -6,6 +6,10 @@ module Homebrew
   module Cleanup
     @disk_cleanup_size = 0
 
+    class << self
+      attr_reader :disk_cleanup_size
+    end
+
     module_function
 
     def cleanup
@@ -21,10 +25,6 @@ module Homebrew
       @disk_cleanup_size += path_size
     end
 
-    def disk_cleanup_size
-      @disk_cleanup_size
-    end
-
     def unremovable_kegs
       @unremovable_kegs ||= []
     end