[FIX] Any environment variable added on Windows must be of type str on py 2
[FIX] Any environment variable added on Windows must be of type str on py 2

Bug: T209767
Change-Id: Ia597b396b007e4299a864f8337238bff823b5ac6

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