Update core.

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

diff --git a/core b/core
index 37c45da..4d68bcd 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit 37c45da5e78e9cd0660ec825447ea117830bf28e
+Subproject commit 4d68bcde441a96abbec1d6c776246c8df323a6b0