Adds failing test post CoffeeScript compilation

Hey, thanks very much for putting this library together. We were hoping to use it for [Harp](https://github.com/sintaxi/harp), but we’re having trouble with compiling CoffeeScript and then minifying in some situations.

I’ve added a simple failing test, basically the following after being compiled:

```coffeescript
() -> alert("hello world")
```

As far as I can tell, UglifyJS handles it okay, but not Minify—but it’s very possible I’m missing something obvious. Thanks!