Fix compatibility with Chef 13

[arm4b]

CI started failing 2 days ago because Chef 12 was replaced by Chef 13 in latest ChefDK.

https://travis-ci.org/StackStorm/chef-stackstorm

[arm4b]

CI is failing due to outdated python dependency for htpasswd cookbook.

It was fixed in sous-chefs/htpasswd#24 by replacing python -> poise-python (thanks @shortdudey123 for the fix).

Waiting for a new version release in https://github.com/redguide/htpasswd/releases

[arm4b]

htpasswd cookbook just released new fixed version https://supermarket.chef.io/cookbooks/htpasswd.

The next CI failure https://travis-ci.org/StackStorm/chef-stackstorm/jobs/234373310 is from pinned version of outdated rabbitmq.
Hope #65 can clear it.