Suppress method redefined warnings

[kou]

% FORCE_FFI_YAJL=ffi ruby -w -I lib -e 'require "ffi_yajl"'
lib/ffi_yajl/parser.rb:33: warning: method redefined; discarding old stack
lib/ffi_yajl/parser.rb:40: warning: method redefined; discarding old key_stack
...

[chef-supermarket]

Hi. I am an automated pull request bot named Curry. There are commits in this pull request whose authors are not yet authorized to contribute to Chef Software, Inc. projects or are using a non-GitHub verified email address. To become authorized to contribute, you will need to sign the Contributor License Agreement (CLA) as an individual or on behalf of your company. You can read more on Chef's blog.

GitHub Users Who Are Not Authorized To Contribute

The following GitHub users do not appear to have signed a CLA:

• @kou

Please sign the CLA here.

[chef-supermarket]

Hi. Your friendly Curry bot here. Just letting you know that all commit authors have become authorized to contribute. I have added the "Signed CLA" label to this issue so it can easily be found in the future.