Poseidon output is coming from capacity part instead of rate part!

According to the [paper](https://eprint.iacr.org/2019/458.pdf), the output must come from the rate part of the final permutation box. But the implementation outputs the first state element which is in the capacity part
https://github.com/iden3/go-iden3-crypto/blob/master/poseidon/poseidon.go#L95