[IMPR] pathlib is not available on Python 2
[IMPR] pathlib is not available on Python 2

- Show a warning that Pywikibot no longer supports older Pythons
- update hash bank line to python3

Change-Id: Ia92638858cb7557357311d4d8ecb29e720a4d314

wikimedia/pywikibot-core,wikimedia/pywikibot-core