fix mac crash on abruptly ended server thread
diff --git a/src/ruby/end2end/sig_int_during_channel_watch_driver.rb b/src/ruby/end2end/sig_int_during_channel_watch_driver.rb
index 8c9fecd..84d039b 100755
--- a/src/ruby/end2end/sig_int_during_channel_watch_driver.rb
+++ b/src/ruby/end2end/sig_int_during_channel_watch_driver.rb
@@ -62,6 +62,8 @@
     raise 'Timed out waiting for client process. It likely hangs when a ' \
       'SIGINT is sent while there is an active connectivity_state call'
   end
+
+  server_runner.stop
 end
 
 main