That guide is over a year old now and I’m afraid it won’t work with our current version. At the moment we don’t have any resources ourselves which provide instructions on changing over to CKEditor.
However from our Awesome-Strapi repo you can find where someone has created a plugin to swap out the editor for ToastUI: GitHub - fagbokforlaget/strapi-plugin-wysiwyg-toastui: ToastUI wysiwyg plugin for strapi
You may be able to adjust this to use CKEditor instead (and if you do I’m sure the community would welcome a plugin itself that does this 
).