changes for react-hooks-fetch-data: cleaner API

[John-Spraul]

Blog post changes for issue #89 on blog_robinwieruch_content.

Based on this comment by Matt Wright:

You can make your fetch hook cleaner by removing

const doFetch = url => {
setUrl(url);
};

and just returning setUrl like so

return [ ...state, setUrl ];

then change your hook call to

const [ data, doFetch ] = useDataApi(
'http://hn.algolia.com/api/v1/search?query=redux',
{ hits: [] },
);

And now you can rename "doFetch" to anything you want```

PR for changes in example code: the-road-to-learn-react/react-hooks-introduction#11

[rwieruch]

There were a few more code snippets to adjust, that's why I just committed the changes myself (see 6ec4f50). Thank you though! Hope I spotted every thing that needed to be changed :)