DataLoader swallows original exceptions

[sebastiandev]

When executing the batch_load_fn if an error occurs, the exception been raised is not the original one, but an Exception which references the original one in its message, like:

Data loader batch_load_fn function raised an Exception: DomainError("Invalid id 'test' in id ",)

My custom exception is a DomainError but it gets lost and re-raised as an Exception

[sebastiandev]

@syrusakbary is anyone maintaining this library? this error is pretty urgent in order to make this production ready.

[syrusakbary]

@sebastiandev if you would like, I'd welcome a PR :)