Update Security String to 2019-09-01
Bug: 137199979
(cherry picked from commit 436498276617e0b45586421464d8f425375982bd)

Change-Id: I9defb8b1af7378a72a1dcfdad7699c9828cbd4fd
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index c8792e9..9054c55 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -250,7 +250,7 @@
     #  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 := 2019-08-05
+      PLATFORM_SECURITY_PATCH := 2019-09-01
 endif
 .KATI_READONLY := PLATFORM_SECURITY_PATCH