* tbody, thead, tfoot - revise role to indicate they are either `rowgroup` or have no corresponding role depending on role of ancestor table element. Update allowed roles to be either ‘none’ if ancestor table is exposed as a table, grid or treegrid.  If not one of those 3 roles, then any role is allowed.
* update tr to note that it is exposed as a row if ancestor table is exposed as a table, grid or treegrid. otherwise on corresponding role.
* update th and td role columns to be consistent.  remove link to HTML AAM in th - it wasn’t in the td one, and we already indicate that implicit semantics are defined in HTML AAM in other areas of the spec.  indicate that th/td have no corresponding role if the ancestor table is not exposed as a table, grid or treegrid

just making some changes to the file to try and mitigate the the Travis build process getting all mucked up again.