Update leinigen to 2.5.1.

The .jar file is now a .zip file but they are the same thing, so we
just install it as a .jar file.

ChangeLog: https://github.com/technomancy/leiningen/releases/tag/2.5.1

Differential Revision: https://reviews.freebsd.org/D1771
Reviewed by: bapt
Approved by: bapt