Reverting Android Security Patch Level string back to 2015-10-01

Change-Id: I0ecc1c9103e7686dffcb8b7009d52aa8d546ae0b
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index a130799..9bb5a2c94 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 := 2015-10-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"