@gp54321https://github.com/plone/mockup/blob/master/CHANGES.rst says TinyMCE was updated to 4.7.6 with mockup 2.7.2. Plone 5.1.1 only has mockup 2.7.1. So either the Changelog in https://github.com/plone/Products.CMFPlone/blob/5.1.x/CHANGES.rst is wrong or this version bump of mockup was missed.
Yes I see now 4.7.6 on your demo site. Must have been a cache problem. You have now Tinymce 4.7.6 in all its glory. Minus the toolbar icons, though.