rubygems.org is slowly to visite in China, Use Taobao source to speen gem install.

More information visit http://ruby.taobao.org/.

Terminal Command

$ gem source -l
*** CURRENT SOURCES ***

https://rubygems.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 jekyll
...