Rails 4.1.0

Upgrade rails 4.0.2 to 4.1.0.

references:
* [upgrade guide](http://edgeguides.rubyonrails.org/upgrading_ruby_on_rails.html)
* [release node](http://edgeguides.rubyonrails.org/4_1_release_notes.html)

### How to upgrade yohoushi

1. Stop yohoushi: `bin/yohoushi stop`
2. Just run `bin/bundle` to upgrade gems
3. Start yohoushi: `bin/yohoushi`