Added: missing express compatibility trick in middleware loading

In express you can add a middleware in two ways:

```coffeescript
app.use express.static __dirname + '/public_client/public', maxAge: 86400000
# or
app.use '/public', express.static __dirname + '/public_client/public', maxAge: 86400000
```
This PR enables the second way (used in the Cozic application).