The `master` repo requires CocoaPods 0.29.0

今天用pod install时出现错误：
The `master` repo requires CocoaPods 0.29.0
但是，终端gem update CocoaPods 显示
Updating installed gems
Nothing to update
原因是gem版本不支持升级至0.29.0
具体见：http://stackoverflow.com/questions/16511705/the-master-repo-requires-cocoapods-0-18-1

解决步骤如下：
sudo gem update
sudo gem install CocoaPods