更换ruby gem 原taobao镜像

taobao Gems 源已停止维护，现由 ruby-china 提供镜像服务 - 开源中国社区

ChenYuans-Air:~ cy$ gem sources
*** CURRENT SOURCES ***

https://ruby.taobao.org/

ChenYuans-Air:~ cy$ gem sources --remove https://ruby.taobao.org/
https://ruby.taobao.org/ removed from sources

ChenYuans-Air:~ cy$ gem source -a https://gems.ruby-china.org/
https://gems.ruby-china.org/ added to sources

ChenYuans-Air:~ cy$ gem source -c
*** Removed specs cache ***

ChenYuans-Air:~ cy$ gem source -u
source cache successfully updated

ChenYuans-Air:~ cy$ gem sources
*** CURRENT SOURCES ***

https://gems.ruby-china.org/