add disabled test for option in optgroup in disabled select

lib/capybara/spec/session/node_spec.rb

@@ -166,6 +166,7 @@ Capybara::SpecHelper.spec "node" do
     it "should see enabled options in disabled select as disabled" do
       @session.visit('/form')
       expect(@session.find('//select[@id="form_disabled_select"]/option')).to be_disabled
+      expect(@session.find('//select[@id="form_disabled_select"]/optgroup/option')).to be_disabled
       expect(@session.find('//select[@id="form_title"]/option[1]')).not_to be_disabled
     end
 

lib/capybara/spec/views/form.erb

@@ -322,6 +322,9 @@ New line after and before textarea tag
       Disabled Select
       <select name="form[disabled_select]" id="form_disabled_select" disabled="disabled">
         <option value="Should not see me" selected="selected">Should not see me</option>
+        <optgroup>
+          <option value="Disabled too">Disabled too</option>
+        </optgroup>
       </select>
     </label>
   </p>