Update Security String to September for Bugfix
(cherry picked from commit d932d49b64fcc794dfd112694dade745eb345363)

Change-Id: I124efe0ec01541e4d825f1fe2d4dba39ad9f9b28
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index 68984d1..dff27df 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 := 2017-04-01
+      PLATFORM_SECURITY_PATCH := 2017-09-01
 endif
 
 ifeq "" "$(PLATFORM_BASE_OS)"