更新gem，源报错bad response Not Found 404 (https://gems.ruby-china.org/specs.4.8.gz)

➜  ~ gem update
Updating installed gems
ERROR:  While executing gem ... (Gem::RemoteFetcher::FetchError)
    bad response Not Found 404 (https://gems.ruby-china.org/specs.4.8.gz)

去了gem https://gems.ruby-china.org 才发现原来是改为了https://gems.ruby-china.com
修改步骤：
删除久源地址

gem sources -r https://gems.ruby-china.org/

添加新源地址

gem sources --add https://gems.ruby-china.com/

确保只有一个源地址

➜  ~ gem sources -l
*** CURRENT SOURCES ***

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

然后就ok了！