Update travis to xenial worker

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

.travis.yml

@@ -1,4 +1,4 @@
-dist: trusty
+dist: xenial
 sudo: required
 # setup travis so that we can run containers for integration tests
 services:
@@ -25,6 +25,7 @@ addons:
       - libprotobuf-c0-dev
       - libprotobuf-dev
       - socat
+      - libseccomp-dev
 
 env:
   - TRAVIS_GOOS=linux TEST_RUNTIME=io.containerd.runc.v1 TRAVIS_CGO_ENABLED=1
@@ -33,8 +34,6 @@ env:
 
 before_install:
   - uname -r
-  - sudo apt-get -q update
-  - sudo apt-get install -y libseccomp-dev/trusty-backports
 
 install:
   - sudo PATH=$PATH GOPATH=$GOPATH script/setup/install-protobuf