Add version number to commander interface

[enriquecaballero]

After moving to semantic-release, we can no longer parse out the version number from package.json. We'll have to come up with a way of injecting the current version number during the build process.

[enriquecaballero]

A few brainstorm notes:
Once unit testing is added in, Travis should run yarn test as its default script. Followed by after_success, yarn semantic-release will run as normal -- we'll just add a prepublish script to build the lib directory that will be published to npm prior to semantic-release's npm publish step. During this prepublish step, we inject the version number from package.json (the one semantic-release wrote in during the pre step) to define the correct --version argv within commander.

[enriquecaballero]

See semantic-release/semantic-release#211.