🐧 Avoid starting xvfb on Linux

...since we don't run tests anymore in there.

.travis.yml

@@ -13,8 +13,6 @@ install:
   - nvm use $NODE_VERSION
   - if [ $TRAVIS_OS_NAME == "linux" ]; then
       sudo apt-get install build-essential git libgnome-keyring-dev fakeroot;
-      export DISPLAY=:99.0;
-      sh -e /etc/init.d/xvfb start;
     fi
 
 script: script/cibuild