rubygems-customization before ruby-windows-devkit

Fixes chef-dk#100

rubygems-customization drops in a custom operating_system.rb, after the devkit install
has modified the regular version of this file. However, if we install the devkit after
we place this file, the devkit will modify the custom version.
Merge pull request #193 from opscode/btm/devkit-fix

rubygems-customization before ruby-windows-devkit