Use last version of core (fix critical bug in wiki permissions).

Signed-off-by: Florent Bruneau <florent.bruneau@polytechnique.org>

diff --git a/core b/core
index 6cc34b5..4f67da2 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit 6cc34b5041e235805e37756b146b86a62f104e2a
+Subproject commit 4f67da27edb0f631a7af1ccf5aa6e7ead84332dc