.travis(.yml): Update to Xenial

Xenial is now available with Travis CI https://blog.travis-ci.com/2018-11-08-xenial-release

.travis(.yml): Update to Xenial
Xenial is now available with Travis CI https://blog.travis-ci.com/2018-11-08-xenial-release
c8020327 · Alexis La Goutte · Tatsuhiro Tsujikawa · 07244434 · c8020327
Commit c8020327 authored 6 years ago by Alexis La Goutte Committed by Tatsuhiro Tsujikawa 6 years ago
--- a/.travis.yml
+++ b/.travis.yml
-dist: trusty
+dist: xenial
 language: cpp
 os:
  - osx