Add php5-xdebug to travis install

Author: joonty

.travis.yml

@@ -6,7 +6,7 @@ rvm: 1.9.3
 notifications:
   irc: "irc.freenode.org#vdebug"
 before_install:
-  - sudo apt-get update && sudo apt-get install vim-gtk php5-cli
+  - sudo apt-get update && sudo apt-get install vim-gtk php5-cli php5-xdebug
 before_script:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"