Using attach results in "The head content contains invalid characters"

Hey, I am trying to attach a file to a request.
```
let stream = fs.createReadStream(f);
r.attach('something', stream);
```

Gives me a seemingly unhandlable error `The header content contains invalid characters`.

Unrelated but I had the same error with `set` when i passed it a hash and ended up being forced to call it for each key value pair.

I'm in node, not a browser.