Does this test against 8 combinations on Travis? Can we cut this down a bit? Maybe like:

```ruby
if RUBY_VERSION >= '1.9.3'
  rails_versions = ['~> 3.2.13', '~> 4.0.0']
else
  rails_versions = ['~> 3.0.20', '~> 3.1.12']
else
```

I doubt there's much difference between Ruby 1.9.2 and 1.9.3 for those Rails 3 versions.