Remove deprecated sudo setting on Travis
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

apache/zookeeper,apache/zookeeper,arshadmohammad/zookeeper,apache/zookeeper,hanm/zookeeper,hanm/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,hanm/zookeeper,apache/zookeeper,hanm/zookeeper,hanm/zookeeper,maoling/zookeeper,maoling/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,hanm/zookeeper,hanm/zookeeper,arshadmohammad/zookeeper,arshadmohammad/zookeeper,apache/zookeeper,apache/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper,hanm/zookeeper,maoling/zookeeper,maoling/zookeeper,apache/zookeeper,apache/zookeeper,maoling/zookeeper,arshadmohammad/zookeeper,maoling/zookeeper