cocoapods 安装出错

安装cocoapods如果遇到以下错误：

Could not find a valid gem 'cocoapods' (>= 0), here is why:
      Unable to download data from http://ruby.taobao.org/ - bad response Not Found 404 (http://ruby.taobao.org/latest_specs.4.8.gz)

可以�使用下面的命令解决此问题：

gem source -r https://rubygems.org/ 
gem source -a http://rubygems.org/
sudo gem install cocoapods