Update ed25519-dalek

[skeet70]

To resolve two potential moderate vulnerabilities, one that doesn't affect us because of a lack of keypair serialization/deserialization, and another timing attack that needs investigation to see if we're indirectly using the affected Sub function.

The update-dalek branch started this process but has test failures that need to be tracked down.

Blocking IronCoreLabs/recrypt-wasm-binding#109