update vkh

diff --git a/vkh b/vkh
index 06e3d523f947d193d4278523ced13c15c1bfbf16..681d3b8f22bf29f04a329464239cabaf38beeb45 160000 (submodule)
--- a/vkh
+++ b/vkh
@@ -1 +1 @@
-Subproject commit 06e3d523f947d193d4278523ced13c15c1bfbf16
+Subproject commit 681d3b8f22bf29f04a329464239cabaf38beeb45