Update core

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

diff --git a/core b/core
index c6e84b6..a217426 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit c6e84b6d8243fd19b8d767c244be789ab45d7401
+Subproject commit a21742678e53db58f3d406e355bf0b60fcd46e19