fix(travis): Added xvfb service to travis config (#203)

.travis.yml

@@ -12,7 +12,6 @@ script:
   npm install -g browserify webpack webpack-cli &&
   node ./scripts/run-module-bundlers-smoketests.js
 - export DISPLAY=:99.0
-- sh -e /etc/init.d/xvfb start
 - echo "RUN integration tests on real browsers" &&
   TRAVIS_CI=true node ./scripts/run-browsers-smoketests.js
 
@@ -23,6 +22,8 @@ addons:
   firefox: 'latest'
   chrome: 'stable'
 
+services: ["xvfb"]
+
 after_script: npm run publish-coverage
 
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