Fix travis CI build.
- Bundler 1.3 needs rbconfig to be required to run `bin/rspec` after installing with `--standalone --binstubs`. bundler/bundler#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.