test/bitgo: `buffer.length` instead of `byteLength`
test/bitgo: `buffer.length` instead of `byteLength`

Not sure how `.byteLength` even worked since it's a method:
https://nodejs.org/api/buffer.html#buffer_class_method_buffer_bytelength_string_encoding

In any case we care about `.length`

BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS,BitGo/BitGoJS