Prepend our Ruby version to PATH
Remove Chef attributes for gem_package
Only update rubygems once
Clarify why we modify PATH
Use ruby-build without chruby as we don't need a version manager

Will install our Ruby to /usr/local so that it's automatically
added to PATH, saving us a lot of environment trouble.
Tweak comment
Merge pull request #9 from elm-city-craftworks/ruby-env

Simplify Ruby setup