updated travis file to install xclip on container

.travis.yml

@@ -3,14 +3,18 @@ notifications:
 
 sudo: false
 
+addons:
+  apt:
+    packages:
+      - xclip
+
 language: node_js
 
 node_js:
   - "4.2"
-
 env:
   - GITHUB_TOKEN=1b17d62d38a4846efa7ea4de4b773b581787b0f1 
-  
+
 before_install:
   - if [ $TRAVIS_OS_NAME == "linux" ]; then
       export CXX="g++-4.9" CC="gcc-4.9" DISPLAY=:99.0;