Added NEWS entry for [<-.data.table changes.
Added NEWS entry for [<-.data.table changes.

Rdatatable/data.table,jangorecki/data.table,vlulla/data.table,jangorecki/data.table,Rdatatable/data.table,jangorecki/data.table,vlulla/data.table,vlulla/data.table,jangorecki/data.table,Rdatatable/data.table,Rdatatable/data.table,vlulla/data.table