Use fixed core.

Signed-off-by: Roland Häder <haeder@hmmdeutschland.de>

diff --git a/core b/core
index a9bcdaef9d5ae0b4109551a12ae3dcac9c862e8c..61b7ad9c067fe69d7f57ba54d3d723ba5909c8b7 160000 (submodule)
--- a/core
+++ b/core
@@ -1 +1 @@
-Subproject commit a9bcdaef9d5ae0b4109551a12ae3dcac9c862e8c
+Subproject commit 61b7ad9c067fe69d7f57ba54d3d723ba5909c8b7