Python requirement for using the lxml parser

[Emmavt]

We had an issue with the line soup = BeautifulSoup(src, 'lxml'), getting the error discussed in this stackoverflow post: https://stackoverflow.com/questions/24398302/bs4-featurenotfound-couldnt-find-a-tree-builder-with-the-features-you-requeste

It seems that this may be a Python versioning error, and required Python 3, or an updated version of the html5lib package. This may be worth adding as a note in the workshop, or including as a requirement in the install section of the notebook.