刪除所有cocoapods gems，
依次執行以下命令：
sudo gem uninstall cocoapods
sudo gem uninstall cocoapods-core
sudo gem uninstall cocoapods-deintegrate
sudo gem uninstall cocoapods-downloader
sudo gem uninstall cocoapods-plugins
sudo gem uninstall cocoapods-search
sudo gem uninstall cocoapods-stats
sudo gem uninstall cocoapods-try
sudo gem uninstall cocoapods-trunk然後安裝最新發布版本：
sudo gem install cocoapods
