build: Enable fast containers on Travis CI

<https://docs.travis-ci.com/user/ci-environment/>
<https://blog.travis-ci.com/2014-12-17-faster-builds-with-container-based-infrastructure/>
<https://docs.travis-ci.com/user/migrating-from-legacy/>

Author: Krinkle

.travis.yml

@@ -1,6 +1,7 @@
+sudo: false
 language: node_js
 node_js:
-  - '0.10'
-  - '0.11'
-  - '0.12'
   - '4.1.1'
+  - '0.12'
+  - '0.11'
+  - '0.10'