Add :reek to guard

Guardfile

@@ -15,7 +15,12 @@ guard :rspec, cmd: 'bundle exec rspec' do
   dsl.watch_spec_files_for(ruby.lib_files)
 end
 
-guard :rubocop do
+guard :rubocop, cmd: 'bundle exec rubocop' do
   watch(/.+\.rb$/)
   watch(%r{(?:.+/)?\.rubocop(?:_todo)?\.yml$}) { |m| File.dirname(m[0]) }
 end
+
+guard :reek, cmd: 'bundle exec reek' do
+  watch(/.+\.rb$/)
+  watch('.reek')
+end