pod安装问题：
1.在终端输入sudo gem install cocoapods命令后，没有反应。此时应该更换ruby镜像源。通过命令$ gem sources --remove https://rubygems.org/
//等有反应之后再敲入以下命令
$ gem sources -a https://ruby.taobao.org/
然后通过命令行$ gem sources -l 查看当前ruby源。
2. 更改ruby源为https://ruby.taobao.org/ 再次输入sudo gem install cocoapods命令后，报错ERROR:While executing gem ... (Gem::RemoteFetcher::FetchError)
SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certificate verify failed (https://rubygems-china.oss-cn-hangzhou.aliyuncs.com/quick/Marshal.4.8/cocoapods-1.0.1.gemspec.rz)
原因应该是https://ruby.taobao.org/源此时出现了问题，于是将源换成了https://gems.ruby-china.org。接下来的cocoapods 正常下载安装。
