nix: bump just and add to common profile

shell.nix

@@ -1,32 +1,12 @@
 with import <nixpkgs> {};
 
 let 
-  just = rustPlatform.buildRustPackage rec {
-    name = "just-${version}";
-    version = "git";
-    src = builtins.fetchGit {
-      url = "https://github.com/casey/just.git";
-      rev = "6430d38a6a489ba4e818b6a892e8bbbbacbfe8f3";
-    };
-
-    cargoSha256 = "0awfq9fhcin2q6mvv54xw6i6pxhdp9xa1cpx3jmpf3a6h8l6s9wp";
-
-    doCheck = false;
-
-    meta = with stdenv.lib; {
-      description = "Just a command runner ";
-      homepage = https://github.com/casey/just;
-      license = licenses.unlicense;
-      maintainers = [ ];
-      platforms = platforms.all;
-    };
-  };
 
 in 
 stdenv.mkDerivation {
   name = "infra-env";
   buildInputs = [
-    just
+    (pkgs.callPackage ./nix/pkgs/just.nix {})
     git-crypt
     vcsh
     gnupg