need to call save on the instance, otherwise we'll regenerate files with a new…

need to call save on the instance, otherwise we'll regenerate files with a new timestamp but the updated_at won't reflect that

lib/paperclip/attachment.rb

@@ -294,7 +294,7 @@ module Paperclip
       saved_only_process, @options[:only_process] = @options[:only_process], style_args
       begin
         assign(self)
-        save
+        instance.save
       rescue Errno::EACCES => e
         warn "#{e} - skipping file."
         false