Fix renderBody in the docs and in table-message.

Since 3.6.0 (as datatable HISTORY states) if you were subscribing to
renderHeader, renderBody, or renderFooter events, they now have to be prefixed
with 'table' (E.g. table.after('table:renderBody', fn).

This commit fixes the example for ColumnWidths class (datatable-column-widths)
and Message initializer (datatable-message), subscribing to table:renderBody.