Log Message:
Update ruby-thor to 0.18.1.

# 0.18.1, release 2013-03-30
* Revert regressions found in 0.18.0

## 0.18.0, release 2013-03-26
* Remove rake2thor
* Only display colors if output medium supports colors
* Pass parent_options to subcommands
* Fix non-dash-prefixed aliases
* Make error messages more helpful
* Rename "task" to "command"
* Add the method to allow for custom package name