message type uri gives a 404 error

When opening a protocol uri _with_ the message type in your browser a 404 error is shown.

This means when you want to view the documentation for the `message` message in the `basicmessage` protocol you need to go to the following url:

```
# this does work
https://didcomm.org/basicmessage/2.0
```

instead of the following url

```
# this doesn't work
https://didcomm.org/basicmessage/2.0/message
```