Node 4.x, 7.x and 9.x are end-of-life
See https://github.com/nodejs/Release#end-of-life-releases

- 4.x is end-of-life since 2018-04-30
- 7.x is end-of-life since 2017-06-30
- 9.x is end-of-life since 2018-06-30

Should we remove support/suggestion for them?

### From

https://github.com/koajs/koa/blob/41257aa91e437149112668dd018aaa2081f98d0d/package.json#L60

### To

```json
"node": "^6.10.1 || ^8.1.4 || 10.x.x" 
```

(Couldn't determine which semver of v10 should we choose)

---

BTW, the docs wrote:

> Koa requires node v7.6.0 or higher for ES2015 and async function support.

As we do not really "require" v7.6.0, should the docs be changed to `suggests node v7.6.0 or higher`?