No underscore allowed in batch ids

[Whalehunter]

Batches couldn't be applied because I had an underscore in the batch ID name which made it invalid. I'd like to ask if its possible that this error could be an exception instead of a silent error. Or maybe better, an error handler that looks at the exceptions from the Mailchimp API. I don't consider myself capable enough to contribute it myself, so I don't know if that is the right answer. But that's what I think this library can improve on.

Edit: Excuse me, its version 2.5.4 (composer). Maybe I talked too soon, I did not try the master on git.