Update did:peer:2 implementation to align with corrections

[dbluhm]

The did:peer:2 implementation used by this demo should be updated to align with corrections made upstream in the specification.

This is a part of a wider interop effort to improve interoperability across DIDComm v2 implementations supporting did:peer:2. An issue documenting this effort can be found here: https://github.com/decentralized-identity/peer-did-method-spec/issues/64