feat: Update path generation in detail index fallback

Co-authored-by: Nick Sweeting <[email protected]>

archivebox/index/json.py

@@ -53,7 +53,7 @@ def parse_json_main_index(out_dir: str=OUTPUT_DIR) -> Iterator[Link]:
                 try:
                     yield Link.from_json(link_json)
                 except KeyError:
-                    detail_index_path = Path(f"{OUTPUT_DIR}/{ARCHIVE_DIR_NAME}/{link_json['timestamp']}")
+                    detail_index_path = Path(OUTPUT_DIR) / ARCHIVE_DIR_NAME / link_json['timestamp']
                     yield parse_json_link_details(str(detail_index_path))
 
     return ()
@@ -155,4 +155,3 @@ def to_json(obj: Any, indent: Optional[int]=4, sort_keys: bool=True, cls=Extende
     return pyjson.dumps(obj, indent=indent, sort_keys=sort_keys, cls=ExtendedEncoder)
 
 
-