Directories - tests could be more complete

The Directories exercise can be solved using

```
server.route({
method: 'GET',
path: '/foo/bar/baz/file.html',
handler: function(request, reply) {
reply.file('public/file.html');
}
});
```

However, the aim of the exercise is to check if a file in /foo/bar/baz/ will be redirected to its equivalent in /public. Another test should be added, with a different file name.