Replace use of findChild with find (#69)

Author: neatc0der

mkdocs_markmap/plugin.py

@@ -121,7 +121,7 @@ def on_page_content(self, html: str, page: Page, **kwargs) -> str:
             code: Tag
             if markmap.name == "pre":
                 pre = markmap
-                code = markmap.findChild("code")
+                code = markmap.find("code")
             else:
                 pre = markmap.parent
                 code = markmap