[ES6] Remove the need for the Symbol polyfill

[oliviertassinari]

Fix #58 and should fix my test here FormidableLabs/radium#552.

@rofrischmann Feedback welcomed.

[oliviertassinari]

I'm not sure to understand why the test fails. No CODECLIMATE_REPO_TOKEN found?

[robinweser]

Huh, that should not be an issue. Well, I can see that there's everything fine. Thanks for your help :)

[oliviertassinari]

@rofrischmann Thanks! I wasn't sure you where going to merge it 😁. That's debatable.

I'm wondering why the npm run test works on this project and not on the radium one.
I can't find any babel-polyfill installed here. Could this be because of babel@5 (here) / babel@6 (radium)?

[robinweser]

True. I'd normally not merge something that breaks the tests, but in this case it is just the code quality tool that fails, perhaps because I've set up the repo, but that'd be ridiculous.

I am not sure if Babel 5 (stage 0) covered the polyfill as well, but could the reason. I know that using babel-node automatically uses the polyfill. Perhaps --compilers js:babel/register as a mocha argument uses these too.

[ianobermiller]

FWIW I definitely prefer Object.keys and avoiding for loops whenever possible :)