If the gemdir is writable, do not use sudo (issue #79).
If the gemdir is writable, do not use sudo (issue #79).

* Always install the most recent version of bundler, so that we satisfy
  rubinius-2.0.0's Gemfile.

boone/ruby-install,bascht/ruby-install,FreedomBen/ruby-install,boone/ruby-install,ngpestelos/ruby-install,PLOS/ruby-install,ngpestelos/ruby-install,firstval/ruby-install,postmodern/ruby-install,regularfry/ruby-install,firstval/ruby-install,bascht/ruby-install,PLOS/ruby-install,FreedomBen/ruby-install,gevans/miner-install,postmodern/ruby-install,regularfry/ruby-install