Changed CLI to utilize Launchy to open the graph

This should patch the error issue I raised a few days ago.  I added a new Spec for the CLI class, updated the code to make the test pass, and added the new dependency on Launchy into the gemspec file.

This is my first pull request, so I've likely made all manner of mistakes.  Please let me know if there's anything I need to correct.
So, I initially tried that, simply adding Launchy as a runtime dependency in the gemspec file.  However, while the code worked locally, when I issued the pull request, Travis CI blew up on me with an error.  I was able to make it pass, but it required me adding this line, as well as adding the `Gemfile.lock` that resulted from running `bundle install` after that change.  The specific errors are in the failed builds above.  I'd love to remove it if it's not necessary, but I don't understand why Travis choked without it.