fix(travis): use service: xvfb instead of launching it manually. inst…

…all libgconf debian package

.travis.yml

@@ -1,13 +1,15 @@
 language: node_js
 node_js: 8.9.1
+services:
+ - xvfb
 before_install:
-- sh -e /etc/init.d/xvfb start
-- export PATH=$HOME/.yarn/bin:$PATH
-- curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.5.1
+ - sudo apt-get install libgconf-2-4
+ - export PATH=$HOME/.yarn/bin:$PATH
+ - curl -o- -L https://yarnpkg.com/install.sh | bash -s -- --version 1.5.1
 script:
-- yarn build &&
- yarn test &&
- yarn test:downstream
+ - yarn build &&
+  yarn test &&
+  yarn test:downstream
 notifications:
  slack:
  on_success: never
@@ -18,5 +20,5 @@ git:
  depth: 3
 cache:
  directories:
- - node_modules
- - ".downstream_cache"
+  - node_modules
+  - '.downstream_cache'