modify to reproduce environment with Gemfile

This rspec files are very old style, so it is not working with this Gemfile. I modified Gemfile to generate old environment to work rspec. I checked my local environment with this Gemfile.

```
[tarr@localhost roma-ruby-client]$ rspec spec/roma/client/client_pool_spec.rb
........*..*...............

Pending:
  Roma::Client::ClientPool client
    # TODO: startup or mock roma server
    # ./spec/roma/client/client_pool_spec.rb:74
  Roma::Client::ClientPool client
    # TODO: check nodes
    # ./spec/roma/client/client_pool_spec.rb:82

Finished in 0.20596 seconds
27 examples, 0 failures, 2 pending
```