Update development gem dependencies
Do not install development dependencies on Travis CI

Install only needed gems to speed up the tests and to save
resources. So collect all non-needed gems to :development
group and skip it on Travis. On the other hand add "rake"
to :test group to install it.
Do not call `librarian clean` while cooking

We have no need to remove the Cheffile.lock nor flush the cache.
As a matter of fact we should respect the versions in the lock file.

Credits for [Patrick Connolly](https://github.com/patcon) for finding
and inspecting the issue on PR #36.
Merge pull request #160 from tmatilai/travis

Do not install development dependencies on Travis CI