You will have to handle the Google Maps zoom_changed
event and set the center to the original center whenever this event is fired
map.addListener('zoom_changed', function() {
map.setCenter(center);
});
Further, this will stop the user from panning the map and then zooming again. If the user pans the map and then zooms it, the map will be reset to center which you might not want. However if the user does not zoom, he/she can normally pan through the map. You may want to clear this event listener for certain cases.
See a codePen here
PS: Use http only and not https while checking this codepen. I spent almost half an hour trying to get this work in JSfiddle but couldn't.