force rspec-rails-version

Hi @effkay,

the specs seem to run now on travis.

The reason for the
```
kuhsaft_development already exists
kuhsaft_test already exists
```

is `bundle exec rake db:create` in the `Rakefile` when calling `rake setup` but for me this is totally fine and we can keep it while it doesn't is a real issue.

Thank you very much,
Alex