Update connection example in README.md

This PR updates the example connection object within the readme to use `hostname` instead of `host`. The problem with using `host` is that any port number provided will be ignored which could cause confusion. 

For example: 
```js
url.format({
  hostname: 'example.com',
  port: 1337, 
  protocol: 'http'
})
// out: http://example.com:1337

url.format({
  host: 'example.com',
  port: 1337, 
  protocol: 'http'
})
// out: http://example.com
```