chore: fix travis configuration

Author: Tasyp

.travis.yml

@@ -1,15 +1,11 @@
 language: node_js
 node_js:
-  - "6"
-addons:
-  firefox: "49.0"
+  - "stable"
+services:
+  - xvfb
 install:
   - npm install
 before_script:
   - npm install -g grunt
-  - "export DISPLAY=:99.0"
-  - "sh -e /etc/init.d/xvfb start"
-  - sleep 3
-  - echo 'America/Los_Angeles' | sudo tee /etc/timezone
-  - sudo dpkg-reconfigure --frontend noninteractive tzdata
+  - export TZ=America/Los_Angeles
 script: grunt