[core] fixing karma timeout error in travis (vmware-archive#666)

Fixes vmware-archive#666.

Signed-off-by: Jeeyun Lim <jeeyun.lim@gmail.com>

.travis.yml

@@ -34,13 +34,7 @@ cache:
 before_install:
   - export CHROME_BIN=chromium-browser
   - export DISPLAY=:99.0
-
-before_script:
-  - npm install -g gemini
-  - npm install -g selenium-standalone
-  - selenium-standalone install
-  - xvfb-run --server-args="-screen 0, 1600x2400x24" selenium-standalone start > selenium.txt &
-  - sleep 5
+  - sh -e /etc/init.d/xvfb start
 
 script:
   - gulp $TEST_SUITE # run unit test, css regression, and css reference in parallel