Use 3.5 nightly in build matrix
Use 3.5 nightly in build matrix

'nightly' now follows Python 3.6
Use '3.5-dev' for Python 3.5 nightly
http://docs.travis-ci.com/user/languages/python/#On-demand-installations

Partially resolves issue #112

jayvdb/mwparserfromhell,wikimedia/operations-debs-python-mwparserfromhell,jayvdb/mwparserfromhell,earwig/mwparserfromhell,SunghanKim/mwparserfromhell,wikimedia/operations-debs-python-mwparserfromhell,gencer/mwparserfromhell,yuvipanda/mwparserfromhell,gencer/mwparserfromhell,jayvdb/mwparserfromhell,jayvdb/mwparserfromhell,yuvipanda/mwparserfromhell,earwig/mwparserfromhell,wikimedia/operations-debs-python-mwparserfromhell,SunghanKim/mwparserfromhell,earwig/mwparserfromhell,SunghanKim/mwparserfromhell,yuvipanda/mwparserfromhell,yuvipanda/mwparserfromhell,SunghanKim/mwparserfromhell,wikimedia/operations-debs-python-mwparserfromhell,gencer/mwparserfromhell,gencer/mwparserfromhell