[doc] Fix config example in MUC doc

documentation/extensions/muc.md

@@ -472,7 +472,7 @@ muc = manager.getMultiUserChat("myroom@conference.jabber.org");
 muc.create("testbot");
 // User1 (which is the room owner) configures the room as a moderated room
 Form form = muc.getConfigurationForm();
-Form answerForm = form.createAnswerForm();
+FillableForm answerForm = configForm.getFillableForm();
 answerForm.setAnswer("muc#roomconfig_moderatedroom", "1");
 muc.sendConfigurationForm(answerForm);
 
@@ -612,7 +612,7 @@ muc = manager.getMultiUserChat("myroom@conference.jabber.org");
 muc.create("testbot");
 // User1 (which is the room owner) configures the room as a moderated room
 Form form = muc.getConfigurationForm();
-Form answerForm = form.createAnswerForm();
+FillableForm answerForm = configForm.getFillableForm();
 answerForm.setAnswer("muc#roomconfig_moderatedroom", "1");
 muc.sendConfigurationForm(answerForm);