Fix warnins in subject and mutation runner

lib/mutant/runner/mutation.rb

@@ -4,10 +4,18 @@ module Mutant
   class Runner
     # Mutation runner
     class Mutation < self
-      include Concord::Public.new(:config, :mutation)
+      include Equalizer.new(:config, :mutation)
 
       register Mutant::Mutation
 
+      # Return mutation
+      #
+      # @return [Mutation]
+      #
+      # @api private
+      #
+      attr_reader :mutation
+
       # Return killer instance
       #
       # @return [Killer]

lib/mutant/runner/subject.rb

@@ -4,7 +4,15 @@ module Mutant
   class Runner
     # Subject specific runner
     class Subject < self
-      include Concord::Public.new(:config, :subject)
+      include Equalizer.new(:config, :subject)
+
+      # Return subject
+      #
+      # @return [Subject]
+      #
+      # @api private
+      #
+      attr_reader :subject
 
       register Mutant::Subject