Fix the Bundler.rubygems.refresh error.

https://github.com/carsomyr/rbenv-bundler/commit/0aebf227aaf45caf5dd49afbfb5d8970c1506e64

Fix this error: 
![qq20140217-2](https://f.cloud.github.com/assets/2240638/2181173/e463533e-9745-11e3-9c21-38fed3ee9d8e.png)