OS X 10.10 Yosemite support

If you've got an active Apple Mac developer account, good news: Boxen is ready for testing on the developer preview releases of OS X 10.10 Yosemite!

This bumps a number of puppet modules and the core gem. Notably, boxen now *requires* at least Puppet 3.7 for Yosemite support, since older versions had a buggy version detection block in one of the core providers.

If you're using [boxen-web](https://github.com/boxen/boxen-web) to deploy your boxen (which you probably are), you *must* upgrade to the latest version because of boxen/boxen-web#64 and boxen/boxen-web#65.

Fixes #612