Log Message:
py-beautifulsoup4: updated to 4.8.1

4.8.1:

* When the html.parser or html5lib parsers are in use, Beautiful Soup
  will, by default, record the position in the original document where
  each tag was encountered. This includes line number (Tag.sourceline)
  and position within a line (Tag.sourcepos).  Based on code by Chris
  Mayo.

* When instantiating a BeautifulSoup object, it's now possible to
   provide a dictionary ('element_classes') of the classes you'd like to be
   instantiated instead of Tag, NavigableString, etc.

* Fixed the definition of the default XML namespace when using
   lxml 4.4. Patch by Isaac Muse.

* Fixed a crash when pretty-printing tags that were not created
   during initial parsing.

* Copying a Tag preserves information that was originally obtained from
   the TreeBuilder used to build the original Tag.

* Raise an explanatory exception when the underlying parser
   completely rejects the incoming markup.

* Avoid a crash when trying to detect the declared encoding of a
   Unicode document.

* Avoid a crash when unpickling certain parse trees generated
   using html5lib on Python 3.