gem_original_require
这个错误很常见！首先要注意，"`gem_original_require': no such file to load" 的重点不是 gem_original_require ，而是后面信息，示例：
./lib/rubygems/custom_require.rb:31:in `gem_original_require': no such file to load -- rdoc/rdoc (LoadError)
从上面示例我们看到 "rdoc" 没有！安装 ruby-rdoc 即可！
