Setup Travis (cucumber, rspec)

This is initial Travis config for thor-cli. It's set up for Ruby 1.9.3 only and the tests pass [1].

The tests are red for 1.8.7, so it's not added. We should discuss if we want to support 1.8.7 and if so, make a sprint task to make thor-cli compatible with 1.8.7 and then make it run on Travis.

[1] https://travis-ci.org/jistr/thor-cli/builds/4304762