Update ubuntu version - Fix vagrant provision failure

A simple `vagrant up` fails. The default image seems to not
have `apt-add-repository`.

Fixed by useing newer version of ubuntu instead of packages

This only affects local development, not travisci.

Author: vigneshsarma

Diff for: Vagrantfile

@@ -2,8 +2,7 @@
 # vi: set ft=ruby :
 
 Vagrant::Config.run do |config|
-  config.vm.box = "precise64"
-  config.vm.box_url = "http://files.vagrantup.com/precise64.box"
+  config.vm.box = "ubuntu/trusty64"
 
   config.vm.provision :shell, :path => "vagrant/provision.sh"
 end