Fix failing cargo-udeps (sigp#5203)

* Attempt to fix nightly build.

* Update Cargo.toml to pin a commit

* Update Cargo.lock

Author: jimmygchen

Cargo.lock

@@ -235,3 +235,6 @@ inherits = "release"
 lto = "fat"
 codegen-units = 1
 incremental = false
+
+[patch.crates-io]
+curve25519-dalek = { git = "https://github.com/jimmygchen/curve25519-dalek.git", rev = "24019783e9bb9dc1464e7e503732f273a69969c6" }