Add Chefstyle to Rake and Gemspec

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

Rakefile

@@ -3,9 +3,14 @@ require 'rspec/core/rake_task'
 
 Bundler::GemHelper.install_tasks
 
+require "chefstyle"
+require "rubocop/rake_task"
+desc "Run Ruby style checks"
+RuboCop::RakeTask.new(:style)
+
 desc "Run all specs in spec directory"
 RSpec::Core::RakeTask.new(:spec) do |t|
   t.pattern = FileList['spec/**/*_spec.rb']
 end
 
-task default: :spec
+task default: [:style, :spec]

mixlib-shellout.gemspec

@@ -15,6 +15,7 @@ Gem::Specification.new do |s|
   s.required_ruby_version = ">= 2.2"
 
   s.add_development_dependency "rspec", "~> 3.0"
+  s.add_development_dependency "chefstyle", "= 0.4.0"
 
   s.bindir       = "bin"
   s.executables  = []