point nbclassic at the classic jupyter_notebook_config path

Author: Zsailer

nbclassic/notebookapp.py

@@ -131,6 +131,11 @@ class NotebookApp(
         """
     ).tag(config=True)
 
+    # Load configuration from classic notebook config file
+    # for backwards compatibility
+    def _config_file_name_default(self):
+        return "jupyter_notebook_config"
+
     static_custom_path = List(Unicode(),
                               help=_i18n(
                                   """Path to search for custom.js, css""")