cocoapod [!] /usr/bin/curl -f -L -o /var/folders/dj/yccslvys6tb53k2vz87djfsh0000gn/T/d20170219-12508-z77a4l/file.zip https://github.com/kylefleming/opencv/releases/download/3.1.0-ios-fix/opencv2.fram

  [!] /usr/bin/curl -f -L -o /var/folders/dj/yccslvys6tb53k2vz87djfsh0000gn/T/d20170219-12508-z77a4l/file.zip https://github.com/kylefleming/opencv/releases/download/3.1.0-ios-fix/opencv2.fram 或者 ssl证书问题

  参考网址： https://ruby.taobao.org

$ gem sources --add https://gems.ruby-china.org/ --remove https://rubygems.org/
$ gem sources -l
*** CURRENT SOURCES ***

https://gems.ruby-china.org
# 请确保只有 gems.ruby-china.org
$ gem install rails

$ bundle config mirror.https://rubygems.org https://gems.ruby-china.org

****关键：
$ sed -i .bak -E 's!https?://cache.ruby-lang.org/pub/ruby!https://ruby.taobao.org/mirrors/ruby!'

 $rvm_path/config/db

问题：
/Library/Ruby/Site/2.0.0/rubygems.rb:270:in `find_spec_for_exe': can't find gem cocoapods (>= 0.a) (Gem::GemNotFoundException)  from /Library/Ruby/Site/2.0.0/rubygems.rb:298:in `activate_bin_path'  from /usr/local/bin/pod:22:in `<main>'

1.$ sudo gem uninstall cocoapods (移除原来的cocoapods)
2.$ sudo gem install -n/usr/local/bin cocoapods   (在osx10.11.5中，安装cocoapods)
3.$ gem sources -l
4. 如果不是https://ruby.taobao.org/就更换为：
$ gem sources --remove https://rubygems.org/    (移除数据源)
$ gem sources -a https://ruby.taobao.org/             (更换数据源)   
$ gem sources -l                            (查看数据源)
5.$ pod setup    (开始安装)

参考：http://www.jianshu.com/p/700d2cce348c