.travis.yml: Use latest stable and LTS versions

The previous versions, 0.10 and 0.11, are years out of date. Using the
latest versions per the Travis docs should fix the build:

  https://docs.travis-ci.com/user/languages/javascript-with-nodejs/#Specifying-Node.js-versions

Author: Bland, Mike

.travis.yml

@@ -1,4 +1,7 @@
 language: node_js
 node_js:
-  - "0.10"
-  - "0.11"
+  - "node"
+  - "lts/*"
+script:
+  - "npm test"
+  - "printf 'Finished testing with Gulp v4; now testing with Gulp v3\n' && npm install gulp@3 && npm test"