Move documentation to the correct place

The documentation needs to be above the method to correctly document the
method.

actionpack/lib/action_dispatch/system_test_case.rb

@@ -7,7 +7,6 @@
 require "action_dispatch/system_testing/test_helpers/setup_and_teardown"
 
 module ActionDispatch
-  class SystemTestCase < IntegrationTest
   # = System Testing
   #
   # System tests let you test applications in the browser. Because system
@@ -80,6 +79,7 @@ class SystemTestCase < IntegrationTest
   # Because <tt>ActionDispatch::SystemTestCase</tt> is a shim between Capybara
   # and Rails, any driver that is supported by Capybara is supported by system
   # tests as long as you include the required gems and files.
+  class SystemTestCase < IntegrationTest
     include Capybara::DSL
     include SystemTesting::TestHelpers::SetupAndTeardown
     include SystemTesting::TestHelpers::ScreenshotHelper