Update Rubocop to RuboCop constant in Rakefile.

Author: fnichol

Rakefile

@@ -6,7 +6,7 @@ require 'kitchen'
 # Style tests. Rubocop and Foodcritic
 namespace :style do
   desc 'Run Ruby style checks'
-  Rubocop::RakeTask.new(:ruby)
+  RuboCop::RakeTask.new(:ruby)
 
   desc 'Run Chef style checks'
   FoodCritic::Rake::LintTask.new(:chef) do |t|