Fix rubocop reported issues

It will take ages till my brain produces 1.9 style syntax :D

lib/mutant/cli/builder.rb

@@ -145,7 +145,6 @@ module Mutant
 
         private
 
-
           # Add cli options
           #
           # @return [undefined]

spec/integration/mutant/rspec_spec.rb

@@ -10,21 +10,24 @@ describe Mutant, 'rspec integration' do
     end
   end
 
+  let(:base_cmd) { 'bundle exec mutant -I lib --require test_app --rspec' }
+
   specify 'it allows to kill mutations' do
-    Kernel.system('bundle exec mutant -I lib --require test_app --rspec ::TestApp::Literal#string').should be(true)
+    Kernel.system("#{base_cmd} ::TestApp::Literal#string').should be(true)")
   end
 
   specify 'it allows to exclude mutations' do
-    Kernel.system('bundle exec mutant -I lib --require test_app --rspec ::TestApp::Literal#string --ignore-subject ::TestApp::Literal#uncovered_string').should be(true)
+    cli = "#{base_cmd} ::TestApp::Literal#string --ignore-subject ::TestApp::Literal#uncovered_string"
+    Kernel.system(cli).should be(true)
   end
 
   specify 'fails to kill mutations when they are not covered' do
-    cli = 'bundle exec mutant -I lib --require test_app --rspec ::TestApp::Literal#uncovered_string'
+    cli = "#{base_cmd} ::TestApp::Literal#uncovered_string"
     Kernel.system(cli).should be(false)
   end
 
   specify 'fails when some mutations are not covered' do
-    cli = 'bundle exec mutant -I lib --require test_app --rspec ::TestApp::Literal'
+    cli = "#{base_cmd} ::TestApp::Literal"
     Kernel.system(cli).should be(false)
   end
 end

spec/unit/mutant/mutation_spec.rb

@@ -4,7 +4,7 @@ describe Mutant::Mutation do
 
   let(:class_under_test) { Class.new(described_class)                                         }
   let(:object)           { class_under_test.new(mutation_subject, Mutant::NodeHelpers::N_NIL) }
-  let(:mutation_subject) { double('Subject', :identification => 'subject', :source => 'original') }
+  let(:mutation_subject) { double('Subject', identification: 'subject', source: 'original')   }
   let(:node)             { double('Node')                                                     }
 
   describe '#code' do

spec/unit/mutant/subject_spec.rb

@@ -12,22 +12,22 @@ describe Mutant::Subject do
   let(:object) { class_under_test.new(context, node) }
 
   let(:node) do
-    double('Node', :location => location)
+    double('Node', location: location)
   end
 
   let(:location) do
-    double('Location', :expression => expression)
+    double('Location', expression: expression)
   end
 
   let(:expression) do
-    double('Expression', :line => 'source_line')
+    double('Expression', line: 'source_line')
   end
 
   let(:context) do
     double(
       'Context',
-      :source_path => 'source_path',
-      :source_line => 'source_line',
+      source_path: 'source_path',
+      source_line: 'source_line',
     )
   end