CI: `sudo` is not required now
CI: `sudo` is not required now

It is not necessary to use the base image `trusty`, which constrains
the available Python versions.

cf. https://docs.travis-ci.com/user/languages/python/

tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control,tulip-control/tulip-control