Build: Speed up the Travis build

Run Travis tests on a container infrastructure to make it start faster.

See http://docs.travis-ci.com/user/workers/container-based-infrastructure/

(cherry-picked from 31f4f8e3f3)

Closes gh-2027

.travis.yml

@@ -1,3 +1,4 @@
 language: node_js
+sudo: false
 node_js:
 - '0.10'