Comment 0 for bug 1799755

In Python 3.7, a DeprecationWarning is issued for attempting to import ABCs from the collections module and in Python 3.8 this becomes an error.

```
$ .tox/python/bin/python -m pip show lxml
Name: lxml
Version: 4.2.5
Summary: Powerful and Pythonic XML processing library combining libxml2/libxslt with the ElementTree API.
Home-page: http://lxml.de/
Author: lxml dev team
Author-email: <email address hidden>
License: BSD
Location: /Users/jaraco/code/yg/support/yg.integration/.tox/python/lib/python3.7/site-packages
Requires:
Required-by: yg.integration
$ python -W error::DeprecationWarning -c "import lxml.html"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/Users/jaraco/code/yg/support/yg.integration/.tox/python/lib/python3.7/site-packages/lxml/html/__init__.py", line 56, in <module>
    from ._setmixin import SetMixin
  File "/Users/jaraco/code/yg/support/yg.integration/.tox/python/lib/python3.7/site-packages/lxml/html/_setmixin.py", line 1, in <module>
    from collections import MutableSet
  File "<frozen importlib._bootstrap>", line 1032, in _handle_fromlist
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/collections/__init__.py", line 52, in __getattr__
    DeprecationWarning, stacklevel=2)
DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
You are using pip version 10.0.1, however version 18.1 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
```