Use the puppet-agent ruby in config_version.rb

Prior to this, the config_version.rb script (used for r10k) attempted to
use the system ruby to parse the script. This caused problems on Puppet
masters that don't have `ruby` in PATH.

This fixes that by hardcoding the puppet-agent's ruby in the shebang.

scripts/config_version.rb

@@ -1,4 +1,4 @@
-#!/usr/bin/env ruby
+#!/opt/puppetlabs/puppet/bin/ruby
 begin
   require 'rugged'
   require 'socket'