Switch to latest core in order to fix auth-groupe-x administration.

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

diff --git a/core b/core
index 3051158..c16eff5 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit 3051158652dd8f7be6a9d726509b2c64b7030f94
+Subproject commit c16eff5c3e6530afbb394a8c971dd5813a6f955d