Add rspec-rails spec suite to travis builds.
Pick a version of rails that can be installed on the ruby version.
Indicate expected responses.
Use the bundler flags of the current dir repo.

They vary a bit. rails doesn't play so nice with
`--standalone` so it 's important that we use
rspec-rails' .travis.yml bundler flags.
RAILS_VERSION needs to be set during bundling, not cloning.
Merge pull request #64 from rspec/add-rspec-rails-to-builds

[WIP] Add rspec-rails spec suite to travis builds.