Add apt update to travis pre-install

Author: joonty

.travis.yml

@@ -5,7 +5,7 @@ python:
 rvm: 1.9.3
 notifications:
   irc: "irc.freenode.org#vdebug"
-before_install: sudo apt-get install vim-gtk php5-cli
+before_install: sudo apt-get update && sudo apt-get install vim-gtk php5-cli
 before_script:
   - "export DISPLAY=:99.0"
   - "sh -e /etc/init.d/xvfb start"