That's been fixed in this commit: https://github.com/bitcoinjs/bitcoinjs-lib/commit/c3528680808f3ae703c37f40a759e2ef75eed882

I'm working on pulling network specific version values out into a single file. Will push to the same branch(https://github.com/bitcoinjs/bitcoinjs-lib/tree/hd-testnet-support) in an hour or two.