fix(encoding): Fix "lxml.etree.SerialisationError: IO_ENCODER" caused by encoding and/or bad characters

Couldn't reproduce it with local tests, but the real example URL that causes the error is http://www.bbc.com/news/business-29431984.

Closes #40
Merge pull request #41 from cronycle/fix/40-IO_ENCODER

fix(encoding): Fix "lxml.etree.SerialisationError: IO_ENCODER" caused by encoding and/or bad characters