Workaround concurrent-ruby bug when forking

concurrent-ruby is failing to notice that our executor threads are dead
after forking.

Author: rafaelfranca

test/test_task.rb

@@ -7,6 +7,8 @@
 Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)
 
 class TestTask < Minitest::Test
+  include ActiveSupport::Testing::Isolation
+
   FIXTURES_PATH = File.expand_path("../fixtures", __FILE__)
 
   def setup