x-code9 cocoapods 错误 RuntimeError - [Xcodeproj] Unknown object version

解决步骤如下：
1.gem source -l

如果显示：

• CURRENT SOURCES *
  https://ruby.taobao.org/
  移除

2.sudo gem install cocoapods

ERROR: While executing gem … (OpenSSL::SSL::SSLError)
hostname “upyun.gems.ruby-china.org” does not match the server certificate

3.gem sources –remove https://ruby.taobao.org/

4.gem sources -a https://gems.ruby-china.org

5.sudo gem update –system

6.sudo gem install -n /usr/local/bin cocoapods –pre