PostgreSQL sequence name for lastInsertId broken

Seems like we havn't noticed that break since we added the table and column identifier quotation.
The problem is that `$this->table` was wrapped into quotes, which finally breaks the computation of the sequence key here https://github.com/bcosca/fatfree/blob/dev/lib/db/sql/mapper.php#L335

original topic here:
https://groups.google.com/forum/#!topic/f3-framework/oGKuosmhI6g