升级mac到10.12之后，pod用不了，查资料发现，https://ruby.taobao.org/已经更换到https://gems.ruby-china.org这个了，于是更换镜像source，
gem source –r https://ruby.taobao.org/
gem source –a https://gems.ruby-china.org
执行sudo gem install -n /usr/local/bin cocoapods
还是报错，有两个错误
第一种报
ERROR:While executing gem ... (OpenSSL::SSL::SSLError)
hostname "gems.ruby-china.org" does not match the server certificate
证书问题，找了半天也没解决
第二种报
ERROR:While executing gem ... (Gem::DependencyError)
Unable to resolve dependencies: cocoapods requires cocoapods-core (= 1.2.1), cocoapods-downloader (< 2.0, >= 1.1.3), cocoapods-trunk (< 2.0, >= 1.2.0), molinillo (~> 0.5.7), xcodeproj (< 2.0, >= 1.4.4), colored2 (~> 3.1), ruby-macho (~> 1.1)
于是开始升级gem，执行sudo gem update --system
接着执行上面的还是不行，最后我把https://gems.ruby-china.org这个替换成
http://gems.ruby-china.org，使得没错，我把https换成http，结果解决了。
