Use URL object instead of custom 
Hi!
I wonder why you use a custom object type "server" to store url parameters. 
I store my own app url into an environment variable, in a entire form.
You could use https://nodejs.org/docs/latest/api/url.html instead.

I'd like to do this:
```
const apiUrl = url.parse(process.env.API_URL);
const grant = new Grant({
  server: process.env.API_URL,  // or
  server: url.parse(process.env.API_URL),
});
```

Instead of this:
```
const apiUrl = url.parse(process.env.API_URL);
const grant = new Grant({
  server: {
    protocol: apiUrl.protocol.slice(0,-1), // remove ':' in url.protocol
    host: apiUrl.host,
  },
});
```

It would be great to use this kind of syntax without breaking all others uses.
Thank you