Run the specs on CentOS 8 now

Signed-off-by: Tim Smith <tsmith@chef.io>

chefignore

@@ -51,10 +51,12 @@ spec/fixtures/*
 test/*
 features/*
 examples/*
+Guardfile
 Procfile
 .kitchen*
 .rubocop.yml
 spec/*
+Rakefile
 .travis.yml
 .foodcritic
 appveyor.yml

spec/spec_helper.rb

@@ -6,5 +6,5 @@ RSpec.configure do |config|
   config.formatter = :documentation # Use the specified formatter
   config.log_level = :error         # Avoid deprecation notice SPAM
   config.platform = 'centos'
-  config.version = '6.8'
+  config.version = '8'
 end