chore: Update .travis.yml - Add Python 3.10 and latest LXML

[phanak-sap]

Update compatibility matrix with new LXML and Python releases

[codecov-commenter]

Codecov Report

Merging #185 (5a0832f) into master (21a99b5) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #185 +/- ##
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Coverage 92.71% 92.71% =======================================
Files 6 6 Lines 2675 2675 =======================================
Hits 2480 2480 Misses 195 195 

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[phanak-sap]

Seems I was overly optimistic, Python 3.10 is from Oct 5, but still not working correctly on Travis.
https://travis-ci.community/t/add-python-3-10/12220/10

[phanak-sap]

There is almost month, where generic python "3.10" is not resolved, see https://travis-ci.community/t/add-python-3-10/12220/10

I will try to use as workaround specific version "3.10.1" + at least bionic distro. There may be worth, with leaving python 3.6, to leave 16.04 Xenial as base distro.