Fix proxy path

This fix considers the actual target path again (which has been ignored).
Is this better fit as written? This matches the convention used throughout the `setupOutgoing` method.

```js
outgoing.path =  options[forward || 'target'].path;
```

This could also be expanded to be written as below. This would likely satisfy the integration testing.

```js
outgoing.path =  options[forward || 'target'].path || '';
```

If we don't like the idea of setting `outgoing.path` as an empty string this could easily be rewritten to be wrapped in some conditionals.