Simplify Travis config

.travis.yml

@@ -1,16 +1,13 @@
 language: node_js
+sudo: false
 node_js:
-  - "0.12"
+  - stable
 addons:
   firefox: latest
 
-sudo: false
+before_script:
+  - npm install web-component-tester
+  - npm install bower
+  - bower install
 
-before_install:
-  - "npm install -g bower"
-  - "bower install"
-  - "npm install -g web-component-tester"
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
-
-script: "wct"
+script: xvfb-run wct