Update core.

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

diff --git a/core b/core
index fbdbbf6..df1ec68 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit fbdbbf639153ce5acc3f68051bf0e4ba1d756022
+Subproject commit df1ec683f930734d7532bd3dc3b10c46da947748