Fix nix support, by upgrading Rust compiler version

[srid]

This PR mainly updates nixpkgs so that we use the newer Rust compiler.

Without this, the devShell won't be able to build local crates, viz.:

❯ nix develop -c cargo build -p dioxus-cli
error: package `normpath v1.2.0` cannot be built because it requires rustc 1.74.0 or newer, while the currently active rustc version is 1.73.0
Either upgrade to rustc 1.74.0 or newer, or use
cargo update -p normpath@1.2.0 --precise ver
where `ver` is the latest version of `normpath` supporting rustc 1.73.0

[jkelleyrtp]

Cool! Thanks!