Update security string to 2015-12-01

Change-Id: I525bab4579449dd285ba87d7ddc9cb36223bf7fd
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 9bb5a2c..63cc4a3 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -103,7 +103,7 @@
   # Can be an arbitrary string, but must be a single word.
   #
   # If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-  PLATFORM_SECURITY_PATCH := 2015-10-01
+  PLATFORM_SECURITY_PATCH := 2015-12-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"