fix tests

Author: pitr-ch

spec/concurrent/executor/ruby_cached_thread_pool_spec.rb

@@ -32,7 +32,8 @@ module Concurrent
         max_threads = subject.length
         sleep(2)
 
-        latch = Concurrent::CountDownLatch.new(1)
+        latch = Concurrent::CountDownLatch.new(2)
+        subject << proc{ latch.count_down }
         subject << proc{ latch.count_down }
         expect(latch.wait(1)).to be true