nix(package): reading version from cargo manifest file

Author: luisnquin

default.nix

@@ -1,7 +1,7 @@
 {pkgs ? import <nixpkgs> {}, ...}:
 pkgs.rustPlatform.buildRustPackage rec {
   pname = "battery-notifier";
-  version = "unstable";
+  version = (builtins.fromTOML (builtins.readFile ./Cargo.toml)).package.version;
 
   src = builtins.path {
     name = "${pname}-source";