Fix packages: use lib instead of stdenv.lib, fix hello-world source

packages/hello-world.nix

@@ -1,22 +1,22 @@
-{ stdenv }:
+{ lib, stdenv }:
 
 stdenv.mkDerivation {
   pname = "hello-world";
   version = "1.0.0";
 
-  src = builtins.fetchurl {
-    url = "https://raw.githubusercontent.com/NixOS/nixpkgs/master/pkgs/tools/hello/hello.c";
-    sha256 = "1p9sc9h1b6k7bk25n5g0w9gwy6fxlkchr5hpmxczg4bvp6jv93q6";
-  };
+  dontUnpack = true;
 
   installPhase = ''
     mkdir -p $out/bin
-    cp $src $out/bin/hello-world
+    cat > $out/bin/hello-world <<'SCRIPT'
+    #!/bin/sh
+    echo "Hello, world!"
+SCRIPT
     chmod +x $out/bin/hello-world
   '';
 
-  meta = with stdenv.lib; {
-    description = "A tiny hello‑world program used as an example package";
+  meta = with lib; {
+    description = "A tiny hello-world program used as an example package";
     license = licenses.bsd2;
     platforms = platforms.unix;
   };

packages/xonsh.nix

@@ -1,4 +1,4 @@
-{ python3Packages }:
+{ lib, python3Packages }:
 
 python3Packages.buildPythonPackage rec {
   pname = "xonsh";
@@ -21,9 +21,9 @@ python3Packages.buildPythonPackage rec {
 
   doCheck = false;
 
-  meta = {
+  meta = with lib; {
     description = "Python-powered shell that combines Python with shell features";
     homepage = "https://xon.sh";
-    license = python3Packages.setuptools.meta.bsd3 or python3Packages.setuptools.meta.license;
+    license = licenses.bsd3;
   };
 }