[CI] Bump Ubuntu to Xenial and use backports PPA for Golang

Author: singhpratyush

.bin/install_apt.sh

@@ -1,3 +1,7 @@
 #!/bin/bash
+
+# PPA for latest go
+sudo add-apt-repository ppa:longsleep/golang-backports
+
 sudo apt-get update
 sudo apt-get install -y $(grep -vE "^\s*#" apt-requirements.txt  | tr "\n" " ")

.travis.yml

@@ -1,4 +1,4 @@
-dist: trusty
+dist: xenial
 sudo: required
 language: node_js
 node_js: