如果你sudo gem install cocoapods时遇到如下问题！😂你有福了！我刚解决。
ERROR: SSL verification error at depth 1: unable to get local issuer certificate (20)
ERROR: You must add /O=Digital Signature Trust Co./CN=DST Root CA X3 to your local trusted store
ERROR: While executing gem ... (Errno::EPERM)
Operation not permitted - /usr/bin/pod
这是原文：http://www.jianshu.com/p/17043faee2e6
安装 ruby环境即可。以下操作我没有用也能够install cocoapods成功！
$ cd $rvm_path/usr/ssl
$ sudo curl -O http://curl.haxx.se/ca/cacert.pem
$ sudo mv cacert.pem cert.pem
