Update security string to 2015-12-01

Change-Id: I2e07d57e457effdcf685203dabfcfefa47c70bf3

core/version_defaults.mk

diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index a130799..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 := 2015-11-01
+  PLATFORM_SECURITY_PATCH := 2015-12-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"