rbenv install 2.0.0-p0 で Ruby 2.0 をインストールし、 rbenv global 2.0.0-p0 で Ruby 2.0 に切り替えて gem list --local を実行したら ERROR: Your gem push credentials file located at: /Users/tnakamura/.gem/credentials has file permissions of 0644 but 0600 is required. You should reset your credentials at: https://rubygems.org/profile/edit if you believe they were disclosed to a third party. というエラーが発生した。パーミッションを変更しないといけないみた