AttributeError: 'ChoiceLoader' object has no attribute 'searchpath'

Hello Oscar,

thank you for the extension, but with a current Jupyter version it is not usable any more :(

The Jupyter extension ipyauth causes the following error, when used with "jupyter labhub" in version 0.9.6 and jupyter version 0.35.6:

[W 2019-05-13 11:38:44.801 SingleUserLabApp notebookapp:1581] Error loading server extension ipyauth.ipyauth_callback.server_extension
    Traceback (most recent call last):
      File "/usr/local/software/jureca/Stages/Devel-2019a/software/Jupyter/2019a-gcccoremkl-8.3.0-2019.3.199-Python-3.6.8/lib/python3.6/site-packages/notebook/notebookapp.py", line 1576, in init_server_extensions
        func(self)
      File "/usr/local/software/jureca/Stages/Devel-2019a/software/Jupyter/2019a-gcccoremkl-8.3.0-2019.3.199-Python-3.6.8/lib/python3.6/site-packages/ipyauth/ipyauth_callback/server_extension.py", line 10, in load_jupyter_server_extension
        web_app.settings['jinja2_env'].loader.searchpath += [
    AttributeError: 'ChoiceLoader' object has no attribute 'searchpath'

This is the same error, which is discussed here: https://github.com/jupyter/nbdime/issues/337#issuecomment-375843270

Best, Jens Henrik