Use the new Travis container infrastructure

http://docs.travis-ci.com/user/migrating-from-legacy/#Why-migrate-to-container-based-infrastructure%3F

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 3b073b2..cdd30d2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,5 +1,6 @@
 language: go
 script: "./test.sh"
+sudo: false
 go:
     - 1.1
     - 1.2