Remove deprecated sudo setting on Travis
[Travis are now recommending removing the sudo tag.](https://blog.travis-ci.com/2018-11-19-required-linux-infrastructure-migration)
_"If you currently specify sudo: false in your .travis.yml, we recommend removing that configuration"_
Author: dengliming <liming.d.pro@gmail.com>
Reviewers: Enrico Olivelli <eolivelli@apache.org>, Andor Molnar <anmolnar@apache.org>
Closes #1351 from dengliming/patch-1
dengliming