message: Use specific nix version to fix cargo audit
diff: @@ -17,6 +17,7 @@ maintenance = { status = "experimental" }
  wasmer-wasi = { version = "2.0.0", path = "../wasi", default-features=false }
  tracing = "0.1"
  minifb = "0.19"
  +nix = "0.20.2"
  ref_thread_local = "0.1"
  serde = "1"
  typetag = "0.1"
  