[flake8] Ignore pep8-naming N807 in page.py
[flake8] Ignore pep8-naming N807 in page.py

- __str__ method depends on python version. Ignore N807 from
  pep8-naming 0.6.1

Change-Id: Idd00f8c58398a3b5a69ba56dbe69e50bfe30ab4a

wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core,wikimedia/pywikibot-core