FIX: Add missing metaclass to Converter

src/caoscrawler/converters.py

@@ -36,7 +36,7 @@ from .structure_elements import (StructureElement, Directory, File, Dict, JSONFi
                                  DictFloatElement, DictDictElement,
                                  TextElement, DictTextElement, DictElement, DictListElement)
 from typing import Dict as Dict_t, List, Optional, Tuple, Union
-from abc import abstractmethod
+from abc import ABCMeta, abstractmethod
 from string import Template
 import yaml_header_tools
 
@@ -255,7 +255,7 @@ def create_records(values: GeneralStore,
     return keys_modified
 
 
-class Converter(object):
+class Converter(object, metaclass=ABCMeta):
     """
     Converters treat StructureElements contained in the hierarchical sturcture.
     """