Run tests automatically on Travis CI build machines

I simply followed the official VS Code documentation below:

https://code.visualstudio.com/docs/extensions/testing-extensions#_running-tests-automatically-on-travis-ci-build-machines

.travis.yml

@@ -0,0 +1,19 @@
+sudo: false
+
+os:
+  - osx
+  - linux
+
+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;
+    fi
+
+install:
+  - npm install
+  - npm run vscode:prepublish
+
+script:
+  - npm test --silent