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
Output a SemVer compliant build version string

We currently use the `:git_describe` version for all chef-client 
projects. This build version format does not respect 
`Omnibus::Config.append_timestamp` which in turn causes two different 
builds to produce packages named identically. This can wreck havoc on 
when packages are published to backends like Omnitruck and Artifactory.