rbenvとかで以下の様なエラーが出た場合の対処法
$ sudo gem install bundle
Fetching: bundler-1.2.3.gem (100%)
Fetching: bundle-0.0.1.gem (100%)
Successfully installed bundler-1.2.3
Successfully installed bundle-0.0.1
2 gems installed
Installing ri documentation for bundler-1.2.3...
Installing ri documentation for bundle-0.0.1...
file 'lib' not found
Installing RDoc documentation for bundler-1.2.3...
Installing RDoc documentation for bundle-0.0.1...
file 'lib' not found
先にrdocをインストールするだけでよい
$ sudo gem install rdoc