Final call: Headers attribute specified on a cell refers to cells in the same table element (a25f45)

Hi All,

The table rule "Headers attribute specified on a cell refers to cells in
the same table element" has the required approvals and is thus going into a
2 week final call, which will end on Feb 25th, 2020.
https://github.com/act-rules/act-rules.github.io/pull/412

Feedback is welcome during this period.

Best
Jey