Expect discv5::enr::NodeId in NodeInfo repsonse

[mrferris]

Due to a change in ethportal_api, trin's representation of a NodeId in a NodeInfo response changed.

This happening in the future will be avoided once #138 is merged

[mrferris]

On second thought, this violates the portal spec, which for this node ID field reads:

description: Hex encoded NodeId of an ENR (a 32 byte identifier).
pattern: ^0x[0-9a-f]{64}$

whereas discv5::enr::NodeId is serializing to an array of bytes.

So the change should be trin-side.