[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

@@ -4,10 +4,12 @@ node_js:
 sudo: required
 dist: trusty
 
-before_install:
- - export CHROME_BIN=/usr/bin/google-chrome
- - export DISPLAY=:99.0
- - sh -e /etc/init.d/xvfb start
- - sudo apt-get update
- - wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
- - sudo dpkg -i google-chrome*.deb
+addons:
+  apt:
+    packages:
+      - google-chrome-stable
+
+before_script:
+  - export DISPLAY=:99.0
+  - sh -e /etc/init.d/xvfb start &
+  - sleep 3