Use pathlib.path for work_dir

Closes #198 (closed)

arkindex_worker/worker/__init__.py

@@ -235,7 +235,7 @@ class ElementsWorker(
                 self.report.error(element_id, e)
 
         # Save report as local artifact
-        self.report.save(os.path.join(self.work_dir, "ml_report.json"))
+        self.report.save(self.work_dir / "ml_report.json")
 
         if failed:
             logger.error(