Fix React::Test::Utils.render_into_document

In react v13, an internal dom component instance is returned instead of an actual dom node

Author: zetachang

lib/react/test/utils.rb

@@ -9,6 +9,8 @@ def self.render_into_document(element, options = {})
 
         if `#{native_instance}._getOpalInstance !== undefined`
           `#{native_instance}._getOpalInstance()`
+        elsif `ReactTestUtils.isDOMComponent(#{native_instance}) && React.findDOMNode !== undefined` 
+          `React.findDOMNode(#{native_instance})`
         else
           native_instance
         end