`url.URL` should be marked as supported from Node.js v6

`url.URL` is marked as supported from Node.js v7.

```
        url: {
            URL: { [READ]: { supported: "7.0.0" } },
       }
```

But in the Node.js docs of v6 I do find this.

https://nodejs.org/docs/latest-v6.x/api/url.html#url_class_url

I think this needs updating.
