[bugfix, tests] Fix Python 3.5.0 AppVeyor installation
[bugfix, tests] Fix Python 3.5.0 AppVeyor installation

Python 3.5.0 silently fails to install because of a conflict with
Python 3.5.4 preinstalled by default. Use fork of the project to fix
the issues until fixed upstream.

Change-Id: I144a769e5621001ed037226f02f2dc8da47c78fc

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