[Tests] Move to Ubuntu 14.04 on Travis CI

PeterDaveHello · PeterDaveHello · commit 89f55e44bbd6 · 2017-03-28T16:58:53.000+08:00
Since Ubuntu 12.04 is pretty old now, it's also going to EOL next month,
maybe we can just move on Ubuntu 14.04 first.
diff --git a/.travis.yml b/.travis.yml
@@ -1,4 +1,5 @@
 language: generic
+dist: trusty
 sudo: required
 addons:
   apt:
