changing parse scope call to a success

I have a use case where I need access to headers in the `parse` call; changing `.then` to `.success` will expose the additional requests params. This shouldn't break default parse behavior, as the first parameter is still `data`
This seems really weird to me as you should have access to headers. `then` returns the raw request object from `$http`, however `success` dereferences the same object into three:

``` coffee
.then (res) ->
  res == {data: {}, headers: {}, config {})

.success (data, headers, config) ->
```