www redirect is broken

I found `hyperstack.org` via another site that was linking to you. However, they linked to [www.hyperstack.org](https://www.hyperstack.org), which has a broken redirect.

Tested in Safari and Chrome on macOS, as well as `curl`. The URL being redirected to is `https://www.hyperstack.org{https://hyperstack.org/}`, which causes browsers to fail to load the page.

> Safari

> Chrome

> curl

```console
< HTTP/1.1 301 Moved Permanently
< Server: Cowboy
< Date: Tue, 09 Mar 2021 16:12:52 GMT
... snip ...
* Connection #0 to host www.hyperstack.org left intact
You are being redirected.* Closing connection 0
```

Steps to reproduce:

- visit https://www.hyperstack.org with a browser

Expected result:

- browser redirects to https://hyperstack.org

Actual result:

- browser fails to load https://www.hyperstack.org{https://hyperstack.org/}