forward Hugo's exit code so this module itself reports success/failure (fixes #77)

lib/cli.js

@@ -6,4 +6,7 @@ import hugo from "../index.js";
 const args = process.argv.slice(2);
 
 spawn(hugo, args, { stdio: "inherit" })
-  .on("exit", process.exit);
+  .on("exit", (code) => {
+    // forward Hugo's exit code so this module itself reports success/failure
+    process.exit(code);
+  });