Fix rubocop warnings in gemspec

* Add bundler as a development dependency

config/rubocop.yml

@@ -3,6 +3,7 @@ AllCops:
     - '../**/*.rake'
     - 'Gemfile'
     - 'Gemfile.devtools'
+    - 'mutant.gemspec'
   Excludes:
     - '**/vendor/**'
     - '**/benchmarks/**'

mutant.gemspec

@@ -1,21 +1,20 @@
-# -*- encoding: utf-8 -*-
+# encoding: utf-8
 
 Gem::Specification.new do |gem|
   gem.name        = 'mutant'
   gem.version     = '0.3.0.beta21'
-  gem.authors     = [ 'Markus Schirp' ]
-  gem.email       = [ 'mbj@schirp-dso.com' ]
-
+  gem.authors     = ['Markus Schirp']
+  gem.email       = ['mbj@schirp-dso.com']
   gem.description = 'Mutation testing for ruby'
   gem.summary     = 'Mutation testing tool for ruby under MRI and Rubinius'
   gem.homepage    = 'https://github.com/mbj/mutant'
   gem.license     = 'MIT'
 
-  gem.require_paths    = [ 'lib' ]
+  gem.require_paths    = %w[lib]
   gem.files            = `git ls-files`.split("\n")
-  gem.test_files       = `git ls-files -- spec`.split("\n")
+  gem.test_files       = `git ls-files -- spec/{unit,integration}`.split($/)
   gem.extra_rdoc_files = %w[TODO LICENSE]
-  gem.executables      = [ 'mutant' ]
+  gem.executables      = %w[mutant]
 
   gem.add_runtime_dependency('parser',              '~> 2.0.0.pre3')
   gem.add_runtime_dependency('unparser',            '~> 0.0.10')
@@ -27,4 +26,6 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency('anima',               '~> 0.0.6')
   gem.add_runtime_dependency('concord',             '~> 0.1.1')
   gem.add_runtime_dependency('rspec',               '~> 2.14.1')
+
+  gem.add_development_dependency('bundler', '~> 1.3', '>= 1.3.5')
 end