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

.travis.yml

@@ -1,5 +1,4 @@
 language: java
-sudo: false
 
 matrix:
   include: