Package for rbenv-ruby-2.0.0-p451

This is not a security update.  Details here:
https://www.ruby-lang.org/en/news/2014/02/24/ruby-2-0-0-p451-is-released/
Upgrade bundled rubygems to 2.1.11

This is to maintain consistency with previous packages for ruby 2.0.0.
Without this, the upgrade of ruby would result in a downgrade of
rubygems to 2.0.14

ruby 2.0.0-p247 shipped with rubygems 2.0.3 which has issues with
bundler[1].  The workaround was to bump rubygems in 414e5ca.

[1] https://github.com/bundler/bundler/issues/2445
Fix rbinstall tool to work with newer rubygems.

The rbinstall.rb tool monkey-patches rubygems.  This monkey-patching
needs to be updated to work with the newer version or rubygems.
Merge pull request #28 from alphagov/rbenv_ruby_200_p451

Package for rbenv-ruby-2.0.0-p451