WIP: Ubuntu 14.04

This updates the cookbook to use a new Vagrant box running Ubuntu 14.04 LTS.

Package updates include:

* Nginx 1.4.6
* PostgreSQL 9.3.4
* Ruby 2.1.1-p76

Note that the new VM works best with **2 GB of RAM and 2 CPUs**, which is much more compared to Ubuntu 12.04.

TODO:

- [ ] Wait for https://github.com/hw-cookbooks/postgresql/pull/125 to be merged upstream
- [ ] Update Test-Kitchen and integration tests