fix rubocop expand path failure

reek.gemspec

@@ -12,7 +12,7 @@ Gem::Specification.new do |s|
   s.license = 'MIT'
   s.email = ['[email protected]']
   s.extra_rdoc_files = ['CHANGELOG.md', 'License.txt']
-  s.files = Dir.chdir(File.expand_path('..', __FILE__)) do
+  s.files = Dir.chdir(File.expand_path(__dir__)) do
     `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features|samples|docs|tasks)/}) }
   end