Update to current suggestion from vscode testing

https://code.visualstudio.com/api/working-with-extensions/continuous-integration#travis-ci

Author: alanz

.travis.yml

@@ -16,12 +16,11 @@ os:
 # This is needed to enable testing VS Code on Travis, as per
 # https://code.visualstudio.com/docs/extensions/testing-extensions#_running-tests-automatically-on-travis-ci-build-machines
 before_install:
-  - if [ $TRAVIS_OS_NAME == "linux" ]; then
-      export CXX="g++-4.9" CC="gcc-4.9" DISPLAY=:99.0;
-      sh -e /etc/init.d/xvfb start;
-      sleep 3;
+  - |
+    if [ $TRAVIS_OS_NAME == "linux" ]; then
+      export DISPLAY=':99.0'
+      /usr/bin/Xvfb :99 -screen 0 1024x768x24 > /dev/null 2>&1 &
     fi
-
 install:
 - npm install
 - npm run vscode:prepublish