Re: [css-flexbox] editorial: fragmenter is undefined

... and css-grid have similar text that should be updated to
read the same as css-flexbox:

https://drafts.csswg.org/css-grid/#pagination
"The following breaking rules refer to the fragmentation container as the
“page”. The same rules apply to any other fragmentation containers.
(Substitute “page” with the appropriate fragmentation container type as
needed.)"

/Mats