[DO NOT MERGE]Update Security String to 2018-04-01 in oc-dev
Bug:73240847
(cherry picked from commit accee92300b551449cca63b5b4de93543a77b854)

Change-Id: I58930e2e535be7d83497b9648c7c4fef51a4a20c
diff --git a/core/version_defaults.mk b/core/version_defaults.mk
index f03d9ba..648a21d 100644
--- a/core/version_defaults.mk
+++ b/core/version_defaults.mk
@@ -181,7 +181,7 @@
     #  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 := 2018-03-05
+      PLATFORM_SECURITY_PATCH := 2018-04-01
 endif
 
 ifndef PLATFORM_BASE_OS