Fix erroneous core update by jacou

Signed-off-by: Raphaël Barrois <raphael.barrois@polytechnique.org>

diff --git a/core b/core
index ef138fd..786bffb 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit ef138fdcc27646d255cb98615c3e64724496c9bd
+Subproject commit 786bffb570bfc2f5ff1dad386a9558501d4c16e8