VB Pretty-lister removes required explicit line continuation in an interpolated string

Format this code:

``` VB
Module Program
    Dim x = $"{ _
            1}"
End Module
```

You get this:

![badcode](https://cloud.githubusercontent.com/assets/116161/6304903/8660ceec-b8dc-11e4-8710-0e08de5a2392.png)
