Switch to latest core (fixed UTs)

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

diff --git a/core b/core
index 707b65d..6dd4e46 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit 707b65dc805f31c3d82fbf3cc13f0a4ab5b653e8
+Subproject commit 6dd4e4616dcd9034c169f460dafed0a87091fec9