Provide mutant specific metrics:mutant task

Rakefile

@@ -1,2 +1,15 @@
 require 'devtools'
 Devtools.init_rake_tasks
+
+namespace :metrics do
+  desc 'Run mutant'
+  task :mutant => :coverage do
+    project = Devtools.project
+    require File.expand_path('../spec/support/zombie.rb', __FILE__)
+    Zombie.setup
+    status = Zombie::CLI.run(%W(::Mutant --rspec-dm2))
+    if status.nonzero?
+      raise 'Mutant task is not successful'
+    end
+  end
+end