Automatic Refreshing - Change Url on each request.

Hi,

First, great library - thanks.

I'm using Automatic Refreshing and would like to update the url before the request is made.

Would it be possible to have the url returned as a function? For example....

```
connect(({ refreshInterval }) => {
return {
dataFetch: {
url: (props) => { return `http://foo.com/${new Date().getTime()}` },
refreshInterval: refreshInterval
}
}
})
```

...or should I be attempting this some other way.

Many thanks.