Support Vagrant's new global commands

Without this change, Vagrant fails to find the JSON file:

/Users/mlafeldt/devel/projects/practicing-ruby-cookbook/Vagrantfile:32:in `read': No such file or directory - chef.json.example (Errno::ENOENT)
	from /Users/mlafeldt/devel/projects/practicing-ruby-cookbook/Vagrantfile:32:in `block (2 levels) in <top (required)>'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.2/plugins/kernel_v2/config/vm_provisioner.rb:72:in `call'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.2/plugins/kernel_v2/config/vm_provisioner.rb:72:in `add_config'
	from /Applications/Vagrant/embedded/gems/gems/vagrant-1.6.2/plugins/kernel_v2/config/vm.rb:281:in `provision'
	from /Users/mlafeldt/devel/projects/practicing-ruby-cookbook/Vagrantfile:26:in `block in <top (required)>'
Update to Berkshelf v3
Add Berksfile.lock
Merge pull request #27 from mlafeldt/berkshelf-v3

Update to Berkshelf v3
Run Travis against 2.1
Use new Vagrant box: Ubuntu Server 14.04 LTS from Canonical

https://vagrantcloud.com/ubuntu/trusty64
Give VM more CPU & RAM
Let Test-Kitchen test against Ubuntu 14.04
Adapt postgresql test