Without this `require 'rubygems'` Brew can't find the Gem.  I did some searching and found this advice on avoiding an explicit `require`: https://gist.github.com/rtomayko/54177.  However, both fixes suggested by this article -- adding `-rubygems` to the Ruby command line, and adding `rubygems` to your `RUBYOPTS` -- are not applicable in our case.  (I noticed that debrew.rb also has an explicit require of rubygems.)

I'm happy to fix this if someone can let me know how.