update kinterbasdb link in docs

[Former user]

The Firebirdsql dialect section of docs provides a link to kinterbasdb Python driver to old sourceforge page, but there is an updated driver (3.3.0) here: http://firebirdsql.org/index.php?op=devel&sub=python

Maybe it contains fixes/features that can be used in SA firebirdsql code.

[Lele Gaifax]

Fixed by 6385, thank you.