Update Security String for bugfix relese to February
(cherry picked from commit 2fd44e18884fe30a18f67a4a1ceb8f5a14d0d6ab)

Change-Id: I184372ad42320ee342c7f2c9decf66cd4555c74f
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 956eafe..0d9dc5d 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -114,7 +114,7 @@
     #  It must be of the form "YYYY-MM-DD" on production devices.
     #  It must match one of the Android Security Patch Level strings of the Public Security Bulletins.
     #  If there is no $PLATFORM_SECURITY_PATCH set, keep it empty.
-      PLATFORM_SECURITY_PATCH := 2018-01-01
+      PLATFORM_SECURITY_PATCH := 2018-02-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"