issue guard#533: subject.stop so thread cannot keep running and lead …

…to raise_expired_test_double_error

spec/lib/listen/adapter/linux_spec.rb

@@ -26,6 +26,10 @@
     # TODO: fix other adapters too!
     subject { described_class.new(config) }
 
+    after do
+      subject.stop
+    end
+
     describe 'watch events' do
       let(:directories) { [Pathname.pwd] }
       let(:adapter_options) { {} }