ports/90020: correct rrdtool dependency

[Renato Botelho]

Synopsis: correct rrdtool dependency

Responsible-Changed-From-To: freebsd-ports-bugs->garga
Responsible-Changed-By: garga
Responsible-Changed-When: Tue Dec 6 13:38:46 GMT 2005
Responsible-Changed-Why: 
Grabbed.

http://www.freebsd.org/cgi/query-pr.cgi?pr=90020