Simplify .travis.yml
Simplify .travis.yml

pip is now looking for wheels by default and create
a wheel if it can't find it for a sdist:

    When no wheels are found for an sdist, pip will
    attempt to build a wheel automatically and insert
    it into the wheel cache.

python/pythondotorg,python/pythondotorg,proevo/pythondotorg,proevo/pythondotorg,manhhomienbienthuy/pythondotorg,Mariatta/pythondotorg,Mariatta/pythondotorg,manhhomienbienthuy/pythondotorg,proevo/pythondotorg,proevo/pythondotorg,Mariatta/pythondotorg,Mariatta/pythondotorg,manhhomienbienthuy/pythondotorg,manhhomienbienthuy/pythondotorg,python/pythondotorg,python/pythondotorg