Support node 4

[zeke]

Successor to #66

[zeke]

This looks good to go. I just realized I'm not an owner of the npm package. Pinging folks to see if I can get added.

[zeke]

@nathansobo hooked me up as an owner.

I bumped the major to be on the safe side.

$ np major
 ✔ Prerequisite check
 ✔ Git
 ✔ Cleanup
 ✔ Installing dependencies using npm
 ✔ Running tests
 ✔ Bumping version using npm
 ✔ Publishing package
 ✔ Pushing tags

 oniguruma 7.0.0 published 🎉

Thanks for making this change, @elingerojo. 👍

[elingerojo]

@ashleygwilliams
@zeke

Thank you both for setting the ball rolling again. I was stalled for this Node 4 support.