Log Message:
py-lxml: updated to 4.2.1

4.2.1:
Bugs fixed
* iterwalk() failed to return the ‘start’ event for the initial element if a \ 
tag selector is used.
* Failure to import 4.2.0 into PyPy due to a missing library symbol.
* Add “-isysroot” linker option on MacOS as needed by XCode 9.