Fix AttributeError: 'Sphinx' object has no attribute 'debug'

[coldfix]

Hi again,

while summarizing a module that has invalid formatting in some docstring, it raises an exception (with sphinx 2.0):

  File "/home/thomas/.local/venvs/madgui/lib/python3.7/site-packages/autodocsumm/__init__.py", line 117, in get_grouped_documenters
    self.env.app.debug('[autodoc] module analyzer failed: %s', err)
AttributeError: 'Sphinx' object has no attribute 'debug'

I believe the debug attribute changed between sphinx versions, and it now just uses a global logger = logging.getLogger(__name__), so we should as well.

[Chilipp]

You are completely right, thank you again