[automerger skipped] [DO NOT MERGE] Update Security String to 2018-04-01 Bug: 73240847 skipped: 5b07fbe498 skipped: ab40f0170c skipped: df3319a7fb skipped: ccd891285c

Change-Id: I8a60ed0ab627fb6dda498e7d2f9993769651c5e3