Support Ruby 1.8.7 for rspec-rails

rspec-rails will be supporting Ruby 1.8.7 for the 3.x line. Ammeter will need to continue support 1.8.7 if it is going to be used by rspec-rails.

This fixes the failing code which was on 1.8.7 (see https://travis-ci.org/rspec/rspec-rails/jobs/33202333). It also updates the build scripts / setup to get the 1.8.7 environments running. This isn't the most elegant solution, :grimacing:, I sort of brute forced things until I got it all working.