Calling defuse_stdlib() raises a DeprecationWarning error with python -W

``` $ python -W error -c 'import defusedxml; defusedxml.defuse_stdlib()' Traceback (most recent call last): File "<string>", line 1, in <module> File "/home/jamison/.local/lib/python3.9/site-packages/defusedxml/__init__.py", line 30, in defuse_stdlib from . import cElementTree File "/home/jamison/.local/lib/python3.9/site-packages/defusedxml/cElementTree.py", line 38, in <module> warnings.warn( DeprecationWarning: defusedxml.cElementTree is deprecated, import from defusedxml.ElementTree instead. ``` ``` $ pip freeze | grep defusedxml defusedxml==0.7.1 ```