granite: fix granite-0.3.0 build with valac >= 0.25.2

This patch ise based on rev 782, wich make granite can build with
valac >= 0.25.2.

Signed-off-by: Yen-Chin Lee <coldnew.tw@gmail.com>
Merge pull request #101 from coldnew/master

granite: fix granite-0.3.0 build with valac >= 0.25.2