Update core

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

diff --git a/core b/core
index 2899129..668cbf4 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit 2899129155afb0cd567c9d1798a4a809c164f5f6
+Subproject commit 668cbf42df8655290abfa1627250e593e1ff6cc7