Fix constant mutation to not emit nil::Const anymnore

* Add proper mutations to constant names

lib/mutant/mutator/node/const.rb

@@ -18,7 +18,8 @@ module Mutant
         # @api private
         #
         def dispatch
-          emit_nil
+          emit_nil unless parent_type == :const
+          emit_self(nil, *children.drop(1))
           children.each_with_index do |child, index|
             mutate_child(index) if child.kind_of?(Parser::AST::Node)
           end

spec/unit/mutant/mutator/node/cbase/mutation_spec.rb

@@ -8,6 +8,7 @@ describe Mutant::Mutator::Node::Noop, 'cbase' do
   let(:mutations) do
     mutants = []
     mutants << 'nil'
+    mutants << 'A'
   end
 
   it_should_behave_like 'a mutator'

spec/unit/mutant/mutator/node/const/mutation_spec.rb

@@ -3,12 +3,13 @@
 require 'spec_helper'
 
 describe Mutant::Mutator::Node::Const, 'const' do
-  let(:source) { 'A::B' }
+  let(:source) { 'A::B::C' }
 
   let(:mutations) do
     mutants = []
     mutants << 'nil'
-    mutants << 'nil::B'
+    mutants << 'B::C'
+    mutants << 'C'
   end
 
   it_should_behave_like 'a mutator'