It's been awhile working on old project which still running on Rails 3.2.22.2 (latest stable Rails 3 branch). Recently we got an updated need to run on the old project. So after checkout the source from github.
checking on my opt directory found no file with name libreadline.6.dylib in it, but there's an upgrade version 7 in the directory. I figure if I could link the file, it could be working and true is, it's working!
ln -s /usr/local/opt/readline/lib/libreadline.7.0.dylib /usr/local/opt/readline/lib/libreadline.6.dylib
Hope this help others! Cheers!