fixes: missing type[] type hint

Author: b1r3k

sdiff/__init__.py

@@ -3,7 +3,7 @@
 from .compare import diff_struct, diff_links  # noqa
 
 
-def diff(md1, md2, renderer=TextRenderer(), parser_cls: MdParser = MdParser):
+def diff(md1, md2, renderer=TextRenderer(), parser_cls: type[MdParser] = MdParser):
     tree1 = parse(md1, parser_cls)
     tree2 = parse(md2, parser_cls)