Broken in bionic for python 3.7

[Bas Zoetekouw]

python3-lxml in bionic (4.2.1-1) is broken for python3.7. It works fine with python3.6. The version from cosmic (4.2.1-1build1) works fine with python 3.7.

╰─▶ dpkg -l python3-lxml | awk '/^ii/ { print $2" "$3 }'
python3-lxml:amd64 4.2.1-1

╰─▶ python3.6 -c 'import lxml.html; print("ok")'
ok

╰─▶ python3.7 -c 'import lxml.html; print("ok")'
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/usr/lib/python3/dist-packages/lxml/html/__init__.py", line 54, in <module>
    from .. import etree
ImportError: cannot import name 'etree' from 'lxml' (/usr/lib/python3/dist-packages/lxml/__init__.py)

╰─▶ dpkg -l python3-lxml | awk '/^ii/ { print $2" "$3 }'
python3-lxml:amd64 4.2.1-1build1

╰─▶ python3.7 -c 'import lxml.html; print("ok")'
ok

╰─▶ python3.6 -c 'import lxml.html; print("ok")'
ok