Focus tests on Node LTS releases

[BigBlueHat]

The Travis file currently lists 0.10, 0.12, and 4.1:
https://github.com/indexzero/http-server/blob/master/.travis.yml#L3-L6

Based on the LTS schedule, I think it's prudent (sane) to:

• drop 0.10
• (possibly) drop 0.12
• add 6.0
• add 8.0 (once Travis is ready for that)

Think that should limit the pain of maintenance a bit. I'm primarily looking for feedback about dropping 0.12.

Thanks!

[franciscop]

Node.js 8.0.0 is dropping in few days, might as well include it. Though it won't be LTS until 6 months later, but it everything goes according to the plan 8.0 => 8.x should be totally compatible.

[BigBlueHat]

Thanks @franciscop! Added it to the list.

[WesleyDRobinson]

In a nodejs.org survey April 2016, ~18% reported using 0.12 in production with 80% scheduled for upgrade to v4 within the year. Maybe 2017 survey results will be released soon and offer more recent data.
Seems safe to drop.

[franciscop]

Version 8.0.0 has been delayed and apparently will be released later this month.

I would drop 0.12 because it doesn't support es6

[BigBlueHat]

#370 has the goods. It's using Node.js 4-7 and removes some cruft from ages past.

Holler if something looks off. 😁