$ gem sources --remove http://rubygems.org/
$ gem sources -a http://ruby.taobao.org/
$ gem sources -l
*** CURRENT SOURCES ***
http://ruby.taobao.org
# 请确保只有 ruby.taobao.org
$ gem install foo
https://ruby.taobao.org/
$ gem sources --remove http://rubygems.org/
$ gem sources -a http://ruby.taobao.org/
$ gem sources -l
*** CURRENT SOURCES ***
http://ruby.taobao.org
# 请确保只有 ruby.taobao.org
$ gem install foo
https://ruby.taobao.org/