py-lxml: update to 4.1.0

4.1.0:
Features added
* ElementPath supports text predicates for current node, like 窶彈.=窶冲ext窶兢窶�.
* ElementPath allows spaces in predicates.
* Custom Element classes and XPath functions can now be registered with a decorator rather than explicit dict assignments.
* Static Linux wheels are now built with link time optimisation (LTO) enabled. This should have a beneficial impact on the overall performance by providing a tighter compiler integration between lxml and libxml2/libxslt.

Bugs fixed
* Requesting non-Element objects like comments from a document with PythonElementClassLookup could fail with a TypeError.

(adam)