Drop babel-runtime requirement

[mclark-newvistas]

Would it be possible to drop babel-runtime from the package.json when targeting nodejs? I am running node 8.4.0 in production right now, and I don't believe babel offers anything which node lacks. Perhaps make it an optional dependency?

I ask because babel-runtime is indirectly causing issues by including core-js, which itself is spamming my terminal. Ideally we can break the dependency here, which should remove spam from my terminal. See babel/babel#10253 for an example of the terminal output, and why they are not able to break the dependency at that level.

[blikblum]

#196 should make it