Use trusty instead of xenial. See travis-ci/travis-ci#7260 (#49)

* Also see RobotWebTools/rosbridge_suite#311

Author: jihoonl

.travis.yml

@@ -1,7 +1,8 @@
 # This config file for Travis CI utilizes ros-industrial/industrial_ci package.
 # For more info for the package, see https://github.com/ros-industrial/industrial_ci/blob/master/README.rst
 
-dist: xenial
+dist: trusty
+sudo: required
 services:
   - docker
 language: generic