knife cookbook test fails...

When I run:

```bash
bundle exec knife cookbook test COOKBOOK
```

I get:

```text
/var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/knife-essentials-0.8.1/lib/chef/knife/raw_essentials.rb:7:in `<class:Raw>': uninitialized constant ChefFS (NameError)
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/knife-essentials-0.8.1/lib/chef/knife/raw_essentials.rb:6:in `<class:Knife>'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/knife-essentials-0.8.1/lib/chef/knife/raw_essentials.rb:4:in `<class:Chef>'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/knife-essentials-0.8.1/lib/chef/knife/raw_essentials.rb:3:in `<top (required)>'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife/core/subcommand_loader.rb:37:in `load'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife/core/subcommand_loader.rb:37:in `block in load_commands'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife/core/subcommand_loader.rb:37:in `each'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife/core/subcommand_loader.rb:37:in `load_commands'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife.rb:114:in `load_commands'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/knife.rb:162:in `run'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/lib/chef/application/knife.rb:123:in `run'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/gems/chef-10.16.4/bin/knife:25:in `<top (required)>'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/bin/knife:23:in `load'
	from /var/lib/jenkins/workspace/chef-hosted/vendor/bundle/ruby/1.9.1/bin/knife:23:in `<main>'
```

- Ruby 1.9.3
- Chef 10.16.4
- KE 0.8.1