Fix travis CI build.

- Bundler 1.3 needs rbconfig to be required to run `bin/rspec` after
  installing with `--standalone --binstubs`.
  https://github.com/carlhuda/bundler/issues/2382
- The Travis VMs no longer have 32-bit JVMs available. Aruba 0.4.11
  forced the -d32 flag. 0.5 just documents it and makes a file available
  to require that will set it. We've updated Aruba here so that the jruby
  ENV vars aren't set automatically; we've kept the flag to disable JIT
  but removed -d32.
- Aruba now has a "the file xyz shoudl contain" step.