Make dk.rb support x64 ruby

I was having difficulty installing ruby & devkit via chocolatey. `ruby dk.rb init` was not finding the installed ruby (which for reference gets put into `c:/tools/ruby200`).

I was attempting this on Windows 2012 R2 x64, in AWS, via eu-west-1 ami-6abd621d.
* Chocolatey 0.9.8.27
* ruby via [chocolatey package 2.0.0.48100](http://chocolatey.org/packages/ruby/2.0.0.48100) (latest at time)
* ruby devkit via [chocolatey package 4.7.2.2013022401](http://chocolatey.org/packages/ruby2.devkit/4.7.2.2013022401) (latest at time)

I discovered that the install-location is stored in a slightly different search path on the machine that I installed to. I assume this is an x86/x64 difference, but don't really know enough about that area to be certain.

My test consisted of
* install ruby2.devkit
* edit dk.rb as diff
* run `ruby dk.rb init`
* observe that it has generated `config.yml` with the install-location to my ruby