update .travis.yml to test with Python 3.5, 3.6
update .travis.yml to test with Python 3.5, 3.6

BubuLK/sfepy,vlukes/sfepy,lokik/sfepy,rc/sfepy,sfepy/sfepy,vlukes/sfepy,rc/sfepy,lokik/sfepy,rc/sfepy,lokik/sfepy,lokik/sfepy,vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,BubuLK/sfepy,sfepy/sfepy