Cargo.toml: add TODO explaning outdated rand deps

Author: mcginty

Cargo.toml

@@ -74,6 +74,7 @@ harness = false
 travis-ci = { repository = "mcginty/snow", branch = "master" }
 
 [dependencies]
+# TODO: Waiting on https://github.com/RustCrypto/traits/issues/1642
 rand_core = { version = "0.6", default-features = false, features = [
     "getrandom",
 ] }
@@ -106,6 +107,7 @@ serde_derive = "1.0"
 hex = "0.4"
 lazy_static = "1.4"
 x25519-dalek = "2.0"
+# TODO: Waiting on https://github.com/RustCrypto/traits/issues/1642
 rand = "0.8"
 
 [build-dependencies]