nodejs 7 和 8 的比较

https://github.com/nodejs/node/blob/master/doc/changelogs/CHANGELOG_V8.md#8.4.0
https://nodejs.org/en/blog/release/v4.0.0/
https://nodejs.org/en/blog/release/v5.0.0/
https://nodejs.org/en/blog/release/v6.0.0/
https://nodejs.org/en/blog/release/v7.0.0/
https://nodejs.org/en/blog/release/v8.0.0/
https://medium.com/@treyhuffine/whats-new-in-node-8-e1cce6539a71