Update Travis build to run on Ubuntu Xenial.

Author: bgrainger

.travis.yml

@@ -1,5 +1,5 @@
 sudo: required
-dist: trusty
+dist: xenial
 services: docker
 
 env:
@@ -24,7 +24,7 @@ env:
 
 before_install:
 - .ci/docker-run.sh $IMAGE $NAME 3307 $OMIT_FEATURES
-- wget -q -O packages-microsoft-prod.deb https://packages.microsoft.com/config/ubuntu/14.04/packages-microsoft-prod.deb
+- wget -q -O packages-microsoft-prod.deb https://packages.microsoft.com/config/ubuntu/16.04/packages-microsoft-prod.deb
 - sudo dpkg -i packages-microsoft-prod.deb
 - sudo apt-get install apt-transport-https
 - sudo apt-get update