Log Message:
sysutils/ruby-chef-zero: update to 15.0.0

Update ruby-chef-zero to 15.0.0.

15.0.0 (2020-02-19)

* remove deprecation warnings for ruby 2.7 #300 (lamont-granquist)

14.0.17 (2019-12-30)

* Move testing to Buildkite #297 (tas50)
* Apply Chefstyle #298 (tas50)
* Substitute require for require_relative #296 (tas50)
* Use Chefstyle gem and move dev deps to the Gemfile #299 (tas50)

14.0.13 (2019-10-07)

* Add ChefZero::Dist to abstract branding details to a single location
  #293 (Tensibai)

14.0.12 (2019-03-19)

* Loosen the mixlib-log depedency + misc cleanup #292 (tas50)