build!: update rmp serde to v1

[jost-s]

rmp-serde is pinned to v0.15.5 and in conjunction with serde produces an unusual serialization for enums, e. g.

An enum in Rust

#[serde(tag = "type", content = "content")]
pub enum Authority {
    Agent(AgentPubKey),
}

serializes to

{
    "type": {
        "agent": null
    },
    "content": "uhCAkRNQ78aF5GvtY3dL4sLR66Xq_VeancOXV79iosN-hZdQ27BwU"
}

instead of

{
    "type": "agent",
    "content": "uhCAkRNQ78aF5GvtY3dL4sLR66Xq_VeancOXV79iosN-hZdQ27BwU"
}

part of holochain/holochain#3598