[WIP] Update lxml and slackclient to versions that supports python 3.8

[amanda11]

No description provided.

[amanda11]

This installs successfully on both focal and bionic, but have been unable to configure live webhooks to verify.

[winem]

Installation of the pack on U20 was successful and I was able to run actions and i.e. send messages to Slack.

For some reason, the rules/sensors do not work as expected. I tried it with different criteria and even w/o any criteria but I see just:

Jun 19 22:31:25 st2vagrant hubot[21316]: [Sat Jun 19 2021 22:31:25 GMT+0000 (Coordinated Universal Time)] DEBUG Received text message in channel: C01HR5WRVB6, from: U01H47PTVL7 (human)
Jun 19 22:31:25 st2vagrant hubot[21316]: [Sat Jun 19 2021 22:31:25 GMT+0000 (Coordinated Universal Time)] DEBUG No listeners executed; falling back to catch-all

in the logs. This may be a user failure. I'll do some more tests with U18 and the current pack without the 3.8 fixes to see if it's reproducable or not.

[winem]

I'm done with my tests and could not find any issue with the fixes. I tested it on bionic and focal.

[amanda11]

@winem Did you confirm if the problem you were having with sensors happened on prioevus verison of pack on U18?

[arm4b]

FYI lxml was updated in #76.

slackclient major version update v3 ->v4 is a breaking change and will break the sensor in this pack:

sensors/slack_sensor.py:4:0: E0401: Unable to import 'slackclient' (import-error)

And so updating the Slack pip to the latest version will require rewriting the slack sensor.

[CLAassistant]

All committers have signed the CLA.