Not sure if version is correct but I'm going off the 1.0.0.Final branch.

Stacks.yaml:

&lgpl http://www.gnu.org/copyleft/lesser.txt
&lgpl21 http://www.gnu.org/licenses/lgpl-2.1.txt

Prestacks.yaml:

&lgpl http://www.gnu.org/copyleft/lesser.txt
&lgpl21 http://www.gnu.org/licenses/lgpl-2.1.html

This should be fixed. Both should use the txt form of the license.