cocoapods "pod install" のエラー

Mac OS X Yosemite にアップグレードし、rbenvでruby2.1.5を導入。
gem install cocoapodsでpodをインストール。
pod installをすると以下のようなエラーが出た。

$ pod install

Analyzing dependencies
/Users/user_name/.rbenv/versions/2.1.5/lib/ruby/2.1.0/pathname.rb:425:in `open': No such file or directory @ dir_initialize - /Users/user_name/.cocoapods/repos (Errno::ENOENT)
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/2.1.0/pathname.rb:425:in `foreach'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/2.1.0/pathname.rb:425:in `children'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/lib/cocoapods/sources_manager.rb:63:in `all'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/lib/cocoapods/user_interface/error_report.rb:130:in `repo_information'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/lib/cocoapods/user_interface/error_report.rb:34:in `report'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/lib/cocoapods/command.rb:58:in `report_error'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/claide-0.7.0/lib/claide/command.rb:300:in `handle_exception'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/claide-0.7.0/lib/claide/command.rb:274:in `rescue in run'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/claide-0.7.0/lib/claide/command.rb:264:in `run'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/lib/cocoapods/command.rb:45:in `run'
	from /Users/user_name/.rbenv/versions/2.1.5/lib/ruby/gems/2.1.0/gems/cocoapods-0.35.0/bin/pod:43:in `<top (required)>'
	from /Users/user_name/.rbenv/versions/2.1.5/bin/pod:23:in `load'
	from /Users/user_name/.rbenv/versions/2.1.5/bin/pod:23:in `<main>'

解決法

最近の環境では以下のコマンドを使う必要があるようです。
pod setup